I am the proud, new owner of a 04 Tacoma D-cab. I used to be a very proud owner of a 02 D-cab.
The only difference that I can tell visiually is the keyless-entry light. The 02 had a visible red light underneath the radio. The 04 has no visible red light at all.
Also on my 04 the doors dont lock automatically once the truck is in gear. My 02 did this. It was a nice feature.