Sometimes this forum makes me shake my head in disgust. The OP said a $600 budget and we get recommendations for a 5D with an L lens?
So some real recommendations around $600 new, are:
XS with kit lens + cheap telephoto like the Tamron 70-300 or a 50mm 1.8.
XSI with only the kit lens
Used, you have a lot of options. I'd probably look at a 20D or 30D with an 18-55 IS or similar lens.