Lightroom's presets in the Develop module are one of the application's best features. Out of the box you get cool effects such as aged photo, antique light, selenium tone, punch, and much more. If you have the Navigator open, then you can mouse over the preset and see a sample of the effect applied to a thumbnail of your image. Great stuff. You can also create your own presets. So if you build an effect that you love, you can easily apply to future images.
Since presets are sharable documents, you can benefit from the creative experimentation of others. I found an excellent resource at Yanik's Photo School, Top Free Lightroom Presets that lists all sorts of terrific stuff. Yanik also shows you how to install LR presets, which I think is a helpful tip unto itself.
If you want the inside scoop on Lightroom, also keep an eye on the Lightroom Journal. It's info straight from the Adobe Lightroom team.