For me the top 5 bands I would like to see in Rockband that currently are not are in it, and if I had to choose 1 album each:
1. Pantera (Vulgar Display of Power)
2. Megadeth (Rust In Peace)
3. Rise Against (Siren Song of the Counter Culture)
4. Social Distortion (White Light, White Heat, White Trash)
5. Slayer (Seasons in The Abyss)
Definitely tough to keep to 5 though.