What other fruits can you use for a crumble?

[BigRedBall]

I made an apple crumble last night. First time since I was 13 years old! It was flipping lovely. My children loved it. Just had some for breakfast too .

Now I have the crumble bug. Can I mix fruits? Which combinations are the best? What's the best fruit to use? Ripe or unripe?

Plum Crumble = plumble
Rhubard crumble = rhumble (as in let's get ready to)
Greengage crumble = grumble
Apple and blackberry = blumble

There's a word for all of them. Grumble is my favourite. I want crumble now really badly!