Most bluetooth keyboard should work with this. I've got an N800, but it should have similar support for bluetooth keyboards. I've got a nice iGo one that I picked up a few years ago. I'd suggest looking them up.

It works pretty well and can trigger certain shortcuts. Not sure if they cut that out in Fremantle (broken in fremantle... I like it).

As for a mouse, I'm pretty doubtful they've added support for that. I remember seeing a mod a while back which allowed you to use a mouse with the tablet, but it didn't work too well and is kind of pointless.

I'd just stick with the touch screen. But really, most bluetooth keyboards work pretty well.

Also: http://talk.maemo.org/showthread.php?t=36540

I remember seeing a couple other threads on this earlier, but I'm not going to put a lot of effort into finding them.

Hope this helps.

Edit: It turns out that it actually isn't officially supported on the N900. Ouch. this should help out a bit though.