Heresy makes "Waspquitoes". They look pretty cool but aren't quite as giant as some of the other suggestions in this thread (they're smaller than humans in terms of sheer bulk, though the wings do make them seem bigger). They're also tricky to assemble, but then again I expect the same goes for a lot of the giant wasp miniatures out there (it seems a given, considering the wings and all).
BTW, I was just asking about the Waspquitoes on TMP a few days ago, and I was pointed to these cool scratchbuilds:
http://warhammer.org.uk/PhP/viewtopic.php?t=21534&start=0Also, depending on what look you're after, it might be worth checking out the various ranges of sci-fi "space bugs". The Revok from Black Tree have some wasp-like aliens, for instance.