As far as D&D goes I have played 1st, 2nd and 3rd editions with FR being my favorite campaign setting (Ravenloft as a close second). I really only played a little of 3e, I was pretty much out of roleplaying at the time. I sold all of my stuff off on ebay a few years back and got some pretty good money for it.
I did play MERPS for a while, after reading the books years ago. I was a fun system, but I found it got a little bogged down with all the tables and charts for different weapon and spell crits. I know at one time http://www.merp.com/
was offering free downloads of all the old MERPS products as long as you signed up. Not sure if they still are.
I think my favorite rpg was Cyberpunk 2020. I played alot and owned most of the modules. My friends and I really enjoyed the gritty, scraping the bottom of the barrel type games, we were never big on the Monty Haul type campaigns. If my players were sleeping in a gutter and had to rob people to pay for food and to support their drug habits, they were happy players