Wow. These are really good Dave. I may have to steal some of these ideas for my own.

That's the idea - go ahead.
Here are some more:
Volume 212. Subcon
Note: A fun level with a relatively safe top battlefield but a dangerous bottom battlefield.
Suggested Music: King Dedede's Theme
13. UFO 001
Note: Inspired by the "Earthbound" games - makes a really good battlefield.
Suggested Music: One of the Mother tracks (Earthbound)
14. UFO 002
Note: Slightly different to UFO 001 - if you like UFO 001, give this one a go too!
Suggested Music: Fountain of Dreams
15. Toybox
Note: Deceptively simple, but an awesome battlefield - I have a number of variants on this theme.
Suggested Music: Flat Zone (Melee)
16. Blaster
Note: It's a "Blaster", it can work as a battlefield - I'll leave it up to you to decide.
Suggested Music: Mute City (Melee)
17. U-Bend
Note: Plumber inspired madness - fun to make your opponent bounce around - but hard to score a KO in the "U-Bend"!
Suggested Music: Super Mario Bros. (Underground)
18. Gigawing
Note: Another "Starship" stage - interesting to play on.
Suggested Music: Something from Starfox/F-Zero
19. Shattered Stairs
Note: I wanted to make a level for "Midna's Lament" - this is the result - not as random as it looks!
Suggested Music: Midna's Lament
20. Windmill Town
Note: The two "Bridges" make this level go from safe to dangerous if you use the "Drop-Blocks" wisely.
Suggested Music: Yoshi's Island
21. Dizzy Windmill
Note: A level inspired by the "Song of Storms" - it's really fun to play!
Suggested Music: Song of Storms
22. Martini
Note: I've been trying to make a tall stage for a while now - this is one seems to work.
Suggested Music: Fountain of Dreams
I may add some more later (unspecified time frame).
[EDIT] BTW - if you do make some of these levels I'd like to hear your feedback on them!