Um, while probably not completely appropriate… I have two servers that have WP on them (and many other things)..
My primary server, that hosts snay.chaosart.com is a Quad UltraSparc II 300MHz, 3GB of RAM and 12x9GB Drives in RAID 1+0, Running FreeBSD 5.2.1. While the WP doesn’t get many hits, that server handles about 350,000 unique hits a month.
The other server is harder to give spec’s for, since it’s virtual. It’s sitting inside of a VMWare ESX server host, with 2x 2.4GHz P4 Xeons, 6GB of RAM and 2x9GB RAID1, 7x18GB RAID5. It’s been allocated 384MB Ram, 2 Procs, and is Running FreeBSD 5.2.1, and get’s about 75,000 unique hits a month. There are 5 other VM’s on that box.