[quote=mach330; how often are you suppose to have them clean? i'm still debating which camera i want....xsi, d60, 40D, or wait for the nikon D90 coming out.[/QUOTE]
You only need to clean a DSLR when you start to see evidence of sensor dust in your images (little black spots usually seen in large areas of uniform color - like sky). I used my 20D for a couple of years before dust became objectionable, but some find they need sensor cleaning monthly. It depends on how frequently you change lenses and how dusty your environment.
As to which camera to buy for your first DSLR: Find one that fits your hands and go cheap. *All* the Nikon and Canon DSLRs are capable of great photos. The higher end ones provide a bit more specialized capability for substantially more money.