dont know of any VST plugins that do timestretching.... that wouldnt really make sense from a real-time perspective. To be honest mate Acid is probably still the best option.... it's piss easy and it's timestretching algorithm is pretty shit hot (it's basically what acid was designed for). Apart from that, wave editors such as wavelab and soundforge have time stretching options, but you'll need to do the maths to work out how much to time stretch it by.
Well yea if you take a hip hop acappela thats 85 bpm and through it on a jungle track thats 180 bpm, you would have to stretch or pitch those vocals another 5 bpms faster inorder to make the sequence sound right. or you could slow down the jungle track, but eh I that is not what I'm looking to do.