God, I wish I had all my Legos. I had all the Blacktron and M-Tron sets, and a ton of the space police and ice explorer sets. Also had a few from that one underwater one, I cant think of the name for the life of me. When I saw this it made me miss all my Legos. Really, I was huge into them.
You should see the rest of my room.

I have something around 300 sets and the walls are all packed with the ones that I have built up. My collection basically consists of pretty much all of the larger Technic sets from 1988 to 2000, most of the Aquazone, Model Team and post-classic Space sets, many Town sets, some classic Space sets, a few of the old Expert Builder sets, two Train sets (that Metroliner and its addon were too cool to pass up when Lego rereleased them a few years ago) and maybe around 4000 spare parts.
i have an arseload of legos in my drawer, but i dont have enough to assemble what i'd like, and i'd really like to get my hands on some older lego technic sets... waaah 
Look on ebay. I got a lot of old sets from there a few years ago. There are still a handful of things I am looking for (a second 6986 Mission Commander, a 6484 F1 Hauler, a 6940 Alien Moon Stalker and if I can snag a new one without paying through the nose, a 6990 Monorail Transport System), but for the most part I now have everything I always wanted as a kid.
For specific parts, try Bricklink. I bought a bunch of stuff from there just last week for my next few projects. You can also get sets from there, although the prices are often a lot higher than ebay.