In reply to iccy: Hiya,
A relatively cheap solution which should keep your ears happy is to buy an iPod-RCA cable. Apple do a reasonable-quality one with a built-in iPod / iPhone charger for around £30. That way you're free to look around for any amp which takes your fancy.
Like anything you can spend a lot more, but this is what I use through a good (but old) Harman/Kardon 5.1 home cinema amp and it does me fine. H/K are (or used to be) one of the few companies to put quality stereo amps in their home cinema receivers. It's not as good as an equivalent-priced stereo unit granted but it ain't bad. Personally though I'd second Graham D's suggestion of looking around for a an old NAD / Arcam / Linn - type stereo unit, as it's cheaper and will sound better anyway.
You might want to look into upgrading any compressed tracks you have to CD quality (192 kbps) or above, as a good amp and speakers will reveal everything on the recording, including over-compression.
If you're determined to go 5.1, as said above, Onkyo do some good kit. Other solid performers include Denon, Yamaha and Marantz. Be patient and it's possible to get real bargains from high-street retailers: you have to haggle though! Look for last year's items, they'll be hanging around and the retailer will want them gone.