I've never used it, but this looks like something along the lines of what you are looking for.
Riemann Sums - Application Center
I've never used it, but this looks like something along the lines of what you are looking for.
Riemann Sums - Application Center
I just tried it, and it works pretty well. The basically all it says to do is load the Student: Calculus 1 package, type your function, right-click it, go to tutors, single-variable calculus, then Riemann Sums. Then just play around with it. You can change a bunch or parameters, then place a graphic in your maple doc. It even has a little animate function.
You don't really even need to download it if you don't want to, just try out the steps that I laid out.