1995: Store bought 486 DX2 66Mhz, with 8MB ram. I later upgraded the ram to 16MB and the processor to a 133Mhz chip.
1997 or 1998: Custom built Pentium MMX 200 Mhz with 32MB of Ram and a Voodoo 2, 8MB videocard. This was my computer for a quite a while in my broke high school days. I eventually bumped the RAM up to 96MB, but I didn't get a true upgrade for 3+ years. This was the golden era of JRPGs, so I didn't really care much about PC gaming beyond Might and Magic and Blizzard titles.
Late 2001: Store bought Pentium 3 1Ghz, with shitty integrated graphics, 128MB ram, and a 40GB HDD. This was a PC bought for me when I started university. I upgraded the RAM to 384MB, and threw a 120GB HDD in it, but I didn't keep this PC for too long.
2002: Custom upgrade to a AMD Athlon 1800. Most of the other components were harvested from my previous rig. The last time I paid someone to put the PC together for me. While I had installed RAM, processors, and optical drives in the past, I was afraid of building an entire rig for some reason. A year later, I added a Geforce 5600 vid card.
2004: My previous rig died in a fire (literally). Serves me right for cheaping out on the PSU. I replaced it with a Pentium 4 (can't remember the model, but at least 3.0GHz) with 512MB RAM. My videocard and HDD were the only salvageable parts, so I kept those.
Early 2006: My first completely new rig in over 5 years. The first rig that I spec'ed out and built myself. I was pretty early to the dual core game with an Athlon X2 3800. At the start, I had a 250GB HDD, 1GB of RAM, and a Geforce 6800. This PC went through a ton of revisions before my next Major rig 3 years later. By the time I retired it, I had 3 HDDs (1TB total), 4GB ram, Athlon X2 5400, and Geforce 8800.
Mid 2009: My current rig more or less. I upgraded to a Phenom X4 945, with 4GB of RAM, and a 1GB Radeon 4870. Moving to a full tower, I had plenty of HDD bays, and became a bit of a Hardrive Hoarder. In addition to the 500GB, and dual 250GB HDDs I already had, I added a 1TB drive to act as my game drive. Fairly early on, I upgraded to Windows 7, and added another 4GB of RAM.
Since then I have made very few changes. I upgraded the videocard to a GTX 560 last summer, and was forced to grab a 2TB HDD when my Steam folder alone broke 700GB (now at 1.2TB). Thanks to the long console generation, this PC has been able to run pretty much anything in half decent settings on my 1080P screen. When that seems ready to change in the next few months, I will probably hold on to this rig for another year. I have a baby on the way, and until my wife finishes her PhD, money isn't flowing.
My next Rig will be a Intel-based machine. Since I am looking at a late 2014/early 2015 build date, I won't even guess what make yet. AMD drivers were shit during the last year I used my HD 4870, so I will probably stick with Nvidia as well, even if they are a bit pricier.
EDIT: I have built several other PCs for other people in the last 7-8 years. My wife's PC has also gone through a few revisions, mostly using cast off parts from my PC.