The STK500 is a starter kit board that is probably the quickest and easiest way to get started.  It has sockets for all DIP versions of the AVR and has an ISP programmer built in. It can not program the 128 or 103 without an adaptor board. It has test LED's, switches and an RS-232 port making it useful for simple testing. It makes a bulky programmer but that is offset by being able to prototype your software in a known-good environment.  If you are using the Mega8 just remember that each I/O bank has only six pins - not 8 - so two LED's will not light up.  You'll also need to buy or find a 9v wall wart as the cheapskates don't include one.

Buy it at Digikey  (P/N ATSTK500-ND) for $130.