Short answer is none unless you've got several thousand dollars to spend.
If you are playing redbook cds mainly, the centre/rear channels will just be duplicates of the 2 main channels. I'd stick to a good 2 channel integrated unless you will be playing mostly multichannel sources.
You can always select an integrated amp that has 2 sets of speaker outputs, then run 4 speakers - 2 front and 2 rear, just make sure the speakers are reasonably easy to drive.
If you are playing redbook cds mainly, the centre/rear channels will just be duplicates of the 2 main channels. I'd stick to a good 2 channel integrated unless you will be playing mostly multichannel sources.
You can always select an integrated amp that has 2 sets of speaker outputs, then run 4 speakers - 2 front and 2 rear, just make sure the speakers are reasonably easy to drive.