10 CSS Tricks You May or May Not Know

1. CSS font shorthand rule
2. Two classes together
3. CSS border default value
4. !important ignored by IE
5. Image replacement technique
6. CSS box model hack alternative
7. Centre aligning a block element
8. Vertically aligning with CSS
9. CSS positioning within a container
10. Background colour running to the screen bottom

for a more in dept breakdown: http://www.evolt.org/article/Ten_CSS_tricks_you_may_not_know/17/60369/
source: Trenton Moss