I made last month over 200 coasters for a silent auction fundrasier coming up in Feb. The possibilities are limitless. That said, I really like the way the coasters turned out using the SU stamp sets: Field Flowers, Medallion, & Serene Sunflowers. A Paper Studio Clear Stamp set called "Flourishes" made a really neat pattern. Gina K's Take Flight butterfly set turns out neat. It allows you to add color with a sponge dauber. I used Sutter Stamps #I-1349 which is a deer in the woods to make a neat monochromatic masculine slant coaster.
Have fun and stamp what you love!