I got my recent acquisitions from Craigslist and eBay. Check your area for local auction companies too. They'll have an email or even snail mail list you can sign up for. Keep an eye out for business liquidations. A few years back I got boxes and boxes of stuff from a local university clearing out old hardware from their IT department at auction. I hear recycling centers are good places, but I've never tried it myself.
Dell Dimension XPS R400, 512MB SDRAM, Voodoo3 2000 AGP, Turtle Beach Montego, ESS Audiodrive 1869f ISA, Dreamblaster Synth S1
Dell GH192, P4 3.4 (Northwood), 4GB Dual Channel DDR, ATI Radeon x1650PRO 512MB, Audigy 2ZS, Alacritech 2000 Network Accelerator