This site has a nice layout, but is sort of confusing to navigate. They have bunches of content on DBZ (almost as much as me ^_^ LOL)

Layout: 9/10
Content: 7/10
Overall: 8/10

                
Fusions:

Fusion Dance: This is a popular fusion. The requirements are to know the fusion dance, have about the same height, and about the same ki level. You must do it flawlessly. Trunks and Goten have used it to become Gotenks, and Vegeta and Goku have used it to become Gogeta.

Potarra Fusion: These aren't as popular. The users must have the kaioshen earrings on at opposite ears. Then they should be fused together. The only users were have been vegeta and goku, but they were split when they were spit out by Majin Buu.

Namek Fusion: This is a fusion where only one body's features are kept. In DBZ Piccolo fused with Kami and they stayed in Piccolo's body. This is pretty much a fusion of Ki only. No requirements but I think only Nameks can use this fusion.