In addition to GDC, which you already noted, there are the spin-off conventions (GDC Europe, GDC China, and GDC Online in Austin, plus the Serious Games Summit).
There's also the LOGIN conference, which caters specifically to online games (casual Facebook games and MMOs, et cetera). You've also got Microsoft's Gamefest and the recently-launched PAX spinoff, PAX Dev.
Then there are the more localized conferences, such as the Christian Game Developers Conference or the Russian Game Developers Conference or something like IndieCade.
Finally, many game developers would also be interested in more generalized programming/software/technology conferences such as Build or GoingNative.
Most conferences offer a variety of different sessions or talks that will cater to a range of skill levels, so you can usually get something out of them if that's your thing. If you are unsure, try browsing the session material from previous years to get a feel for what the conference might involve -- many of them are expensive so it's good to have an idea of what you're going to get out of them beforehand.
I personally feel like the best benefit from most of the conferences I ever attended was networking, and not so much the sessions themselves -- unfortunately, very often lectures and presentations will be necessarily high-level. But the people you meet can be valuable contacts elsewhere in your career.