you can use a regular metronome for simple triple meter stuff (3/8 etc...) and the compound meters (9/8, 12/8..) All you need is an accented click for those. You could use a drum machine if you want to do the real odd meters.
I've had fun setting that to a totally random collection of tones in some long odd grouping (say 17 - anything too long to keep track of w/o practice) and just playing regular scales and trying to follow the accents as they fall all over the place. Helps me keep time but it doesn't sound so dull.
I actually discovered the weird metronome here on TGP ... I couldn't find the original thread, but thanks are due to somebody around here!