As you probably know, J2ME in its most basic form doesn't support floating point operations. This can be a problem if you are trying to develop games for it.
I've been looking around for alternatives, and found that most sites reference you to MathFP (the link I had seems to be broken, google for it), which is a fast library to do fixed point math. The problem with it is that for certain types of calculations, fixed point can be complicated, given that it is hard to represent numbers that are too small or too large, and mix those in the same calculation.
Browsing around I found MicroFloat, which is a very nice floating point library written entirely in Java. The only gotcha is that it requires long support from the KVM.
There are other libraries around (which I havent tested) such as Real Java.
Well, now to start that doom clone for my cell phone...