Forum Moderators: open
If only one or two key expressions then Google Adwords might be good.
However, if you have some time on your side there are a number pages that have good page ranks that offer very cheap advertising but it is very hit and miss and takes time
Cheers
[edited by: agerhart at 2:04 pm (utc) on Aug. 12, 2003]
[edit reason] removed product promo per TOS [/edit]