Another game I tried recently that works real nice is The Troubleshooters, which works off a BRP derivative.
The core mechanic is dead simple: roll d100 equal to or below your skill to succeed. On opposed rolls, the highest successful roll wins (tie if both fail) – often called "Pendragon rolls". If you roll doubles, that's a roll with "karma", which can be good karma (if you succeed) or bad karma (if you fail). Karma means something extra happens, which may or may not be related to the success or lack thereof of the original roll.
The first twist is how this interacts with difficulties. Difficulties are expressed as + or - a certain number of "pips". If you're rolling at +/- a certain number of pips, any roll where the ones is between 1 and that number is an automatic success or failure. So if your skill is 63, and you're rolling at -2, you will succeed on a roll of 03-10, 13-20, 23-30, 33-40, 43-50, 51-60, or 63.
The second twist is that you can flip a roll, meaning you turn the ones into tens and vice versa (so a 73 turns into a 37). This usually costs 2 "story points", a metacurrency you have a rather limited starting amount of, and which you can get more of by getting into trouble. You can also have Abilities, which fill the same function as feats and often let you flip certain rolls for 1 story point instead.