I second the recommendation that you check out a drop of pond water. Do you have any protoslow (sp?)? Protoslow is this cool stuff that gets motile microorganisms on slides to hold still so you can see them!
Check out water from different areas of a nearby pond or stream. Try to take samples from as wide a variety of aquatic habitats as possible. Rushing water, slowly moving water, and stagnant water are all very different environments, so they’ll each yield different micro-menageries of wee beasties. The water near the top of a lake or stream is a very different place for a critter to set up shop than the water near the bottom is. Therefore, you get a different grab-bag of critters if you sample at different depths. Water that has any kind of scum or coloration in it often has some pretty cool stuff in it, too.
If you’re not completely terrified of insects, spiders, and their various creepy-crawly cousins, check out various bug body parts. They’re pretty amazing. Really! And see if you can get yourself some water bears. (There are some good web pages with instructions for finding and looking at the little guys. Try Googling “tardigrada” and see what you come up with.) If you’d like suggestions for how to catch a bewildering array of incredibly cool teeny-tiny critters you didn’t even know existed, I’d be happy to help you out. Just send me an e-mail, and I’ll tell you anything you want to know about collection methods. (Incidentally, most ways of catching these little guys are cheap, low-tech, and don’t require a heck of a lot of effort.)
In spring and summer, check out the little stalks that come up on the grass in your lawn. Grasses have flowers, although they’re very small, and most people don’t notice them. Some of them look incredibly gorgeous under magnification. So do lots of fungi.
If you’d like, you can take a look at some of your own cells by swabbing the inside of your cheek and rolling out the resulting residue stuff onto a slide.
Have fun with your new toy!