You've come to the right LAF member for information. I have a thread from a year or two back with more information if you can find it. However, there are three main ranges to look into:
Old Glory 25s Bluemoon range - probably the best range for variety of poses and LOTS of mounted figures to go with the dismounted figures (find Deano's thread on painting Old West, somewhere in that thread he has painted samples of a lot of the range). These are larger 15 mm figures, some might call them 18 mm.
Peter Pig has a very diverse range but they are small figures and would not mix great with the above - but they have stuff no one else does.
Freikorps (QRF) Yellow Ribbon Range is also a good place to peruse. These would be middle sized.
Some also rans would be Minifigs. And Hovels, even smaller than Peter Pig. CP models have some very nice figures that would work with Old Glory a little better than Peter Pig.
Again, find my old thread if you can, lots more information.
Let us know if you need more information.