There are a number of adapters that go from a mini headphone plug to a pair of RCA plugs, some marketed specifically for iPods. You'll want to get one that has a long enough cable so you can connect the RCAs to the back of your amp and still have the headphone end somewhere convenient for your iPod.
I'd love to see a Dock with an RCA output and a power input, so I could play my iPod through my stereo as long as I wanted.