I'll echo the love for 2004. One of my favorite games.
But I'm shocked at the lack of hype for 2006. One of the best viewing games ever made. Simple or the audience to keep track of (only confusing aspect was the "scoring periods" and when the automatic score keeping didn't work), and incredibly fun to watch.
http://www.thebluealliance.com/match/2006cmp_f1m2
And, of course, the legendary 138-137 IFI SF1-2 match. The best match ever played in my opinion.
http://www.youtube.com/watch?v=MtkW3V7IEGs
Semi-related to viewing, the most fun I've ever had participating in an event was 2007 Galileo. When Rack'N'Roll was played the style it was on Galileo that year, it was one heck of a game to play and watch. Pity Einstein didn't have a similar style.