Can anyone recommend one? Budget of maybe £50-80. I'm not that nit-picky about the sound and whilst a nice range of different sounds would be great, I'm most keen that it can do really heavy (think Isis in the heavy bits) thick distortion suitable for metally post-rocky stuff.

I was thinking Boss simply because I've never had one fail on me and the build quality is good, so looking at either the DS-2 or ML-2
http://www.soundslive.co.uk/product~name~Boss-ML-2~ID~5787.asp

I realise that actually trying them would be a good idea but opinions would be great.