I have always been a fan of roleplaying games from the beginning of my memories (which start about four years ago, as I am somewhat forgetful these hectic days). Anyway, to get back on subject, I have always been a fan of roleplaying games for a while, and I have found several (good) and one (excellent) roleplaying system on the web. Here I shall list several lists of roleplaying games, and the totally incredible and underhyped (secret!) location of "Coron's Sources of Free RPG", the best (ever, in my opinion) place to find anything that is on the web related to roleplaying.
First, I shall list the few actual systems that I tried and found to be greater than (perhaps), some of the other games on the lists. Here they are, comprising examples from each of the main categories of engine available on the web, namely Big, Small, and Weird.
I also fondly remember the first free game which I tried, the UGE (Universal Gaming Engine), without which this page would have never come into existence.
The roleplaying collections that I favour are:
Coron's Sources (of (free, most of the time) Roleplaying Games)
Coron's entire website is incredible, and you would probably not regret spending a few hours viewing his entire area.
Ericg's Roleplaying collection
Ericg's work was also groundbreaking, although Coron seems to have cut him "to the quick" in some respects. After you check out Coron's place above, you should view his also, to make sure that you haven't missed anything (although that isn't really very likely, with Coron behind the wheel).
Here are a few (incomplete) documents that I wrote a while ago. Perhaps they might be useful, perhaps not. Only view them if you feel adventurous (and don't mind HTML syntax errors!).
Link to index file.