The tool I've heard of before was called Bitcoin Off-The-Grid
, though I think there may be others now.
There's also vanitygen
, which I've found useful occasionally just running "vanitygen 1" to get a random private key with associated address, but that doesn't help you if you have a private key already.
Edit: Oh, and I can't believe I forgot pywallet
. That may be what you're really looking for. Just as a disclaimer, the only one of these I've used personally is vanitygen; but I just haven't needed the others yet.