Most people have heard of SXSW! It's been going on since I was free & footloose (many yrs ago). Fewer outside of Austin, Texas know of the Interactive portion of the festival. Its popularity has waxed and waned along with the dot com economy in Austin, but if you're in the field of multimedia development, it's the place to be in March! Especially if you also like live music and film.
Check it out at www.sxsw.com/