You'll get differing opinions on this, but I've got a PODxt Live that I use as a backup and for recording sometimes, and I think it's great. You have to spend some time setting it up, but I can get good tone with it - it's not the same as my rack gear, but for a fraction of the price it does a very good job.

The PODxt and BOSS GT8 were both pretty good - I went for the POD solely because it's outputs suited my recording setup better. There are also far higher spec units that are amazing, but they have price tags to match...