after getting tired of buying countless cans of compressed air, and then only finding them empty when i need one I bought a little 3 gal compressor on sale at ctc for ~$60 ... came with air gun and tire filler attachment.
It is small enuf to carry to where the rig is but I prefer to carry the rig (most are caseless) out to the garage and blow till its clean. All the dust/hair stays outside.
Does a nice job of blowing the dust out of psu's as well.
I only have a couple of rigs in cases (sons', duaghters') and they take a bit more work and don't clear out as well. also hard to get some hsf's cleared out without removing them or their fans.