Today I would use a regular p3 with whatever chipset I could get. When the next generation of ASL is out, I would go for a dual processor system with a scsi disk subsystem and possibly with machine redundancy - IF I was in charge of a larger corporate network.
For a sub 100 user network, I think the aforementioned p3 would do just fine.
Regarding NICs, I must say that 3com have never failed me, and I think they are the safest bet - ALWAYS. I use some realtek based NICs too, but I don't have that much experience with them except that they are working fine.
If you're not building a machine yourself, I'd recommend taking a look at the new Gigabyte rack boxes. Depending on the reseller, you can buy them complete with drives and CPUs, or as barebones boxes to add things yourself. In the UK, Scan do some good deals.
BTW, I'm not affiliated with either company, but I installed one of their appliance servers for my sister's office, and I may buy one of the single CPU 1U's for myself for Xmas...
[ 19 November 2001: Message edited by: YuppieScum ]