I know I'm late to the party on this one, but I have a few. The first that comes to my mind is that Majin Vegeta vs. Goku fight. That was just an all-out slug fest, and it had a lot more emotional backing than many Z fights. I always liked the ones where Goku shows up and completely cleans house, like against Nappa and the Ginyus. I love the Goku and Pikkon fight, just plain epic. I also think the most just plain entertaining fight was Super Saiyan Vegeta owning Android 19, laughed my ass off pretty much the whole time. Gohan vs. Cell is kinda obvious, don't really need to go into that one. I really liked the Fat Buu vs. Super Saiyan 3 Goku one too. Plus SS3 Goku vs. Janemba cuz it was just such a spectacle. Goku's fight with Cell was pretty cool too, just has such a "come the f*ck on!" abrupt end to it.
In short, I love a lot of em, but my top 3 are Majin Vegeta vs. Goku, Goku vs. Pikkon, and Vegeta vs. Android 17. With honorable mention to Gohan vs. Cell.