I have had fairly good luck building workstation and server configurations with the following components. I can't guarantee that you will too, nor that any of the companies here will remain "best buys" forever. I will try, when I can, to keep this list up-to-date but cannot obviously guarantee that it will be at any given time.
The ASUS P55T2P4 motherboard appears to be a good choice for mid-to-high range Pentium server and workstation systems. You might also wish to investigate ASUS's 486SP3G offering if it's a 486-class motherboard you're looking for (Note: These have become increasingly hard to get as ASUS apparently no longer manufactures them).
Those wishing to build more fault-tolerant systems should also be sure to use Parity memory or, for truly 24/7 applications, ECC memory. Note that ECC memory does involve a slight performance trade-off (which may or may not be noticable depending on your application) but buys you significantly increased fault-tolerance to memory errors.
At the higher end, the Intel/Venus Pro ( VS440FX) motherboard appears to work very well with FreeBSD, as does its accompanying 200Mhz P6 (Pentium Pro) CPU. Recent price drops have dropped P6 systems into a very affordable price bracket, at least in the United States, and for serious server applications you may wish to look no further than the Pentium Pro. My personal `make world' times dropped from 3 hours and 40 minutes with a P5/166 to 1 hour and 22 minutes when I upgraded to a P6/200 machine - not a fair comparison, to be sure, but just to note that in terms of increased productivity, the P6/200 has definitely been worth the upgrade for me.
NOTE: The Intel motherboards are designed to a different form-factor and hence require an entirely different PC case, the so-called "ATX" case design. Consider this fact carefully if you're thinking of upgrading an existing system - all the commonly available ATX cases I've seen so far have been in the "midi-tower" class, with limited space for drives or other internal peripherals available. On the plus side, most ATX cases appear to be of much higher quality than their typical PC counterparts.
The only known interoperability problem with the VS440FX chipset (also known as ``Natoma'') is that the Matrox Meteor frame-grabber board will lock up your system if used in one of these motherboards. Matrox blames Intel, Intel blames Matrox, all we know is that it definitely doesn't work. That is the only card I've had any troubles with in my P6 system and the card works just fine in my older Triton chipset based motherboard.
This one is a bit trickier, and while I used to recommend the Buslogic controllers unilaterally for everything from ISA to PCI, now I tend to lean towards the Adaptec 1542CF for ISA, Buslogic Bt747c for EISA and Adaptec 2940 for PCI.
The NCR/Symbios cards for PCI have also worked well for me, though you need to make sure that your motherboard supports the BIOS-less model if you're using one of those (if your card has nothing which looks even vaguely like a ROM chip on it, you've probably got one which expects its BIOS to be on your motherboard).
If you should find that you need more than one SCSI controller in a PCI machine, you may wish to consider conserving your scarce PCI bus resources by buying the Adaptec 3940 card, which puts two SCSI controllers (and internal busses) in a single slot.
In this particular game of Russian roulette, I'll make few specific recommendations except to say "SCSI over IDE whenever you can afford it." Even in small desktop configurations, SCSI often makes more sense since it allows you to easily migrate drives from server to desktop as falling drive prices make it economical to do so. If you have more than one machine to administer then think of it not simply as storage, think of it as a food chain!
I do not currently see SCSI WIDE drives as a necessary expense unless you're putting together an NFS or NEWS server that will be doing a lot of multiuser disk I/O.
My SCSI preferences extend to SCSI CDROM drives as well, and while the Toshiba XM-3501B (also released in a caddy-less model called the XM-5401B) drive has always performed well for me, I'm now a great fan of the Plextor PX-12CS drive. It's a 12 speed drive with excellent performance and reliability.
Generally speaking, most SCSI CDROM drives I've seen have been of pretty solid construction and you probably won't go wrong with an HP or NEC SCSI CDROM drive either. SCSI CDROM prices also appear to have dropped considerably in the last few months and are now quite competitive with IDE CDROMs while remaining a technically superior solution. I now see no reason whatsoever to settle for an IDE CDROM drive if given a choice between the two.
At the time of this writing, FreeBSD supports 3 types of CDR drives (though I believe they all ultimately come from Phillips anyway): The Phillips CDD 522 (Acts like a Plasmon), the PLASMON RF4100 and the HP 4020i. I myself use the HP 4020i for burning CDROMs (with 2.2-current - it does not work with 2.1.5 or earlier releases of the SCSI code) and it works very well. See /usr/share/examples/worm on your 2.2 system for example scripts used to created ISO9660 filesystem images (with RockRidge extensions) and burn them onto an HP4020i CDR.
I've had pretty good luck with both 8mm drives from Exabyte and 4mm (DAT) drives from HP.
For backup purposes, I'd have to give the higher recommendation to the Exabyte due to the more robust nature (and higher storage capacity) of 8mm tape.
If you can also afford to buy a commercial X server for US$99 from Xi Graphics, Inc. (formerly X Inside, Inc) then I can heartily recommend the Matrox Millenium card. Note that support for this card is also getting better with the XFree86 server, which is available free of charge, though it's still a fair bit slower than the XiG product at this time. I'm told that support is also a fair bit better in the 3.2A release of XFree86, but it's not yet available for general release.
You also certainly can't go wrong with one of Number 9's cards - their S3 Vision 868 and 968 based cards (the 9FX series) also being quite fast and very well supported by XFree86's S3 server.
I have had very good luck with the Sony Multiscan 17SE monitors, as have I with the Viewsonic offering in the same (trinitron) tube. For larger than 17", all I can recommend at the time of this writing is to not spend any less than U.S. $2,500 for a 21" monitor if that's what you really need. There are good monitors available in the >=20" range and there are also cheap monitors in the >=20" range. Unfortunately, very few are both cheap and good!
I can recommend the SMC Ultra 16 controller for any ISA application and the SMC EtherPower or Compex ENET32 cards for any serious PCI based networking. Both of the PCI cards are based around DEC's DC21041 Ethernet controller chip and other cards using it, such as the Zynx ZX342 or DEC DE435, will generally work as well. For 100Mbit networking, either the SMC SMC9332DST 10/100MB or Intel EtherExpress Pro/100B cards will do a fine job.
If what you're looking for is, on the other hand, the cheapest possible solution which will still work reasonably well, then almost any NE2000 clone is a good choice.
If you're looking for high-speed serial networking solutions, then Digi International makes the SYNC/570 series, with drivers now in FreeBSD-current. Emerging Technologies also manufactures a board with T1/E1 capabilities, using software they provide. I have no direct experience using either product, however.
Multiport card options are somewhat more numerous, though it has to be said that FreeBSD's support for Cyclades's products is probably the tightest, primarily as a result of that company's commitment to making sure that we are adequately supplied with evaluation boards and technical specs. I've heard that the Cyclom-16Ye offers the best price/performance, though I've not checked the prices lately. Other multiport cards I've heard good things about are the BOCA and AST cards, and Stallion Technologies apparently offers an unofficial driver for their cards at this location.
I currently use the Gravis Ultrasound MAX due to its high sound quality and full-duplex audio capabilities (dual DMA channels). Support for Windows NT and OS/2 is fairly anemic, however, so I'm not sure that I can recommend it as an all-around card for a machine that will be running both FreeBSD and NT or OS/2. In such a scenario, I might recommend the Creative Labs AWE32 instead.
For video capture, there's really only once choice - the Matrox Meteor card. FreeBSD also supports the older video spigot card from Creative Labs, but those are getting somewhat difficult to find and the Meteor is a more current generation frame-grabber with a higher-speed PCI interface. Note that this card will not work with motherboards based on the VS440FX chipset! See the motherboard reference section for details.