You need to tell us why you feel like you need to upgrade. The system you have currently is enough to play pretty much any game, and do office tasks, so the question is, what do you want more for ? Are you looking for drastic improvements in framerate ? (Probably require new CPU + Mobo + GTX 670 or 680 at least) Faster video encoding or better video editing performance ? Something else ?
Gigabyte Z77x d3h is a good mobo. another choice can be the MSI G43. Go with a Z75 or Z77 mobo, so you can O'C the 3570k if neccesary. When O'C, dont use the stockcooler, get a Scythe Gen 3 double cooler with perfect performance