PDQ/PDQ# for RP intense games.
Hero for well built, rounded characters.
I like 3.5 DnD system, and anything d20 based.
Gerps is the spawn of a very notsome person in my honest opinion.
I've gotten a lot of mileage out of the old TSR Marvel Super-heroes over the years. Yeah, this one's an antique, and it has huge limitations, but they did some really clever things with using abilities in unusual ways. Made for some imaginative gameplay, and I still pull it out from time to time.
The old World of Darkness system worked well for my group too. We're especially fond of Mage (again, a very versatile system).
I never got around to putting a Nobilis game together, but I really like the system here. It's another open ended system, where players can literally do anything, and it's diceless as well. Loads of potential, but a steep learning curve.
I'm not a huge fan of D&D, and most of the reasons are built into every generation of the system. Alignment's probably my biggest bugbear. Definable, objective Good and Evil really get in the way of my storytelling and roleplaying, and the mechanic doesn't lift out easily, so it can't be ignored.
D&D's the system I started on, but I haven't played since Reagan was in office. (Fine, it was AD&D, if you want to get all technical. Satisfied?) One of my group recently convinced me to give it another go, and I'll be starting a 3.5 campaign in the next few weeks, so we'll see if I can make it work for me.