Can you list some off for me? something like Yellow After the Rain...well, I don't know much.
I got Rain Dance and I'm gonna buy Marimba Flamenca for later. I'm not any good though. haha.
just some must-play four mallets, regardless of difficulty.

I know it's been a while since you posted this, but if you are working hard, a good piece to aim for would be "Black Sphinx" by Leander Kaizer. It has an incredible sound to it and any audience will eat it up. You need a marimba with a low 'F' (4 1/2 octaves). After that, anything by Keiko Abe is always a good choice.

Can anybody recommend some difficult marimba literature that is written for a 4.5 octave marimba (low F). I have been playing pieces like My Lady White, Variations on Japanes Childrens songs, etc. so anything in that range is sought. Thanks!

Frogs by Keiko Abe. Intense piece.