The rumours I'm seeing (fairly recent, in the last 2 weeks) are all saying September or October. Probably correct, as I'm sure Apple wants to catch the Christmas market.
Generally, rumours point to a thinner iPad, possibly narrower border/bezel (bigger screen?) but I haven't seen a lot else on features yet.
Rumours of new MacBook Pros are flying around too - for the same time frame, with the new Haswell processors, and support for 4K monitors, though Apple doesn't have any of those yet.
Tim Cook has said that there will be new things to be excited about in the latter half of 2013. Somewhere in there will be the new Mac Pro too.