I had my teeth professionally whitened back in high school, and it was great! I got SO many compliments on my teeth afterwards! My mom worked for a dentist, though, so I'm not really sure how much it cost and I'm sure I wouldn't be able to afford it now.
I just started using Crest White Strips about a week ago. I am seeing a difference, but not as much as I'd like. You wear them for two weeks though, so I'm hoping that by this time next week I'll be satisfied with the results.