I've been doing karate for a little while now, and I am interested in starting to train with some weapons. Does anyone have any advice on which weapons are fun to work with? I'm thinking bo staff, but I'd also like to something a little more original.

Don't use kitchen knives!!!

 I say because i am a black belt that u should use the nunchucks or the bo

im in the same position, and have been adviced that the bo is the starting point and that all other weapons are compared to it, i like the look of the tonfa though

I agree with the bo.  It's seemed to me to be the safest and easiest for people just starting out in weapons to learn even if they have martial art training.  I love the nunchakus as well but as tolsonator mentions above it is a very good starting point and if you study it a while then go to some other weapons you will see how it rolls over to them as well. God bless!