After far too long, I've finally found a new roleplaying group. We're using Dungeon World, a lightweight system I've never used before. It's a class-based system, which I've never been too fond of, but it does seem like it gets rid of most of the things I hate about class-based systems. The core book only gives the standard D&D-style classes, but they give some guidelines on making up your own classes. For my character I worked with the GM to come up with a new Assassin class which combines some of the traits of the Thief and the Fighter. I tried to make sure it's balanced against the other classes and doesn't obviate the Thief/Fighter, but not having used DW before it's hard to be sure. If you've used DW and have any comments, I'd be interested in hearing them.
Edit: I've posted a new version which adjusts the damage option for the Death Dealer and Assassin's Strike moves. Also included is a discussion about how different ways of doing DD/AS would affect DPS, which is necessary for doing a fair comparison against other classes. If you run a game with this class, let me know how it goes.