I just went to take a peek at the Specials on the I Brake For Stamps site. One sheet is all realistic trees, one is inspirational verses, etc., one is scenic and people, one is the coolest group of animals in interesting poses - giraffes, frogs, an ostrich, one of dogs, one of bugs, and then there are some singles up also including two sizes of hibiscus, and some very cool Southwest. It's a great selection! If any of this sounds like something you might need to fill in a gap, go check out the 'Specials' page.
And along those lines, check out Kimm's blog for a tutorial on scenic stamping to help you use all those cool images together.