On The Code Project, Trenton Moss lists 10 very easy and usefull CSS tricks:

  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

Read it al on CodeProject.