Not to steal the thunder of the OP, but there is a great app called Metron which I got yesterday. It's extremely sophisticated; it essentially functions as a rhythm sequencer. You can program whatever click you like, with multiple time signatures, silent bars, accents wherever you like. And you can export a sequence to your computer to back it up, and thus use it on whatever device you like (after converting to mp3). Definitely worth checking out.I bought it. I mean the thing is 99 cents for f--k sake. Now it only has to be better than a candy bar and I'll consider it a worth while expense. I have an iPad permanently located in my drum room and this app will definitely get used there. Sorry that I had to out myself as a mindless consumer pussy in front of everyone. Oh, the shame of it!
BTW, this has almost all of the features I am looking for and it has a straight forward design. If you consider upgrading it, I really want an app that supports polyrhythms. So, it would be cool to have an option to say, place an additional accent sound every three beats, on top of what is already going on. So, I could still have a standard 4/4 thing with a 3 over 4 accent on top of that.
A nice trainer option that goes beyond that would be to have the option to phase between the two meters. Something like: over 8 bars you shift the volume balance between the 4/4 and 3/4 accents so that you can practice hearing and feeling both meters in the same exercise, which is hugely valuable for really nailing the feel.