Cool thread idea! Edited this post in retrospect, since everyone else took the opportunity to mention what they have too much.
SPARCstation 1+, 25 MHz, 64 MB, two Hawk drives, FDD, on-board AUI transceived into RJ45, still fixing the NVRAM and PROM issues, but will run 2.5.1 eventually.
SPARCserver 20, Dual 180 MHz HyperSPARC, 512 MB RAM, QFE, Sun Video SBUS card, 73 gig root, 50 gig option drive. Uplink via two 100 MBit links, this be my home server.
nice to play with. Have spares to run it as Dual 75 MHz, plenty of backup RAM and replacement QFE board, PSU, backplane, internal cabling and sleds, if ever something decides to break. It'll be as cool, just slower.
Too much, can go for cheap
501-2015 FastSCSI / buffered ethernet, 5 EUR
501-2253 TGX+ framebuffer, 5 EUR
501-2708 SuperSPARC, 50 Mhz, 5 EUR
525-1377 OpenBoot PROM, SM71+, 2 EUR