Kiey posted in another thread about making a list of the best anime dubs. So, why not just start one?
First off, Cowboy Bebop and Ghost in the Shell: Stand Alone Complex both have excellent dubs, and I know many people who find the English dub equal and superior to the Japanese.
Second off, FLCL has an amazing English voice cast, and they did a fantastic job translating and localizing cultural references so that they make sense. Another thing that makes this dub special is that the Japanese director worked with the English dubbers when they were writing the script and recording in the studio. This made the English dub exactly what the original director intended.
Thirdly, pretty much any dub by Synch-Point. I haven't heard all of them, but the ones I have heard have all had a high standard of quality.
So, get some anime dubs and dubbing companies down in writing now, and perhaps later we can get a definitive of the best dubs going.