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Other than the inclusion program with Inktomi, if you are selling to the USA market, you don't need anything else.
Yahoo PFI in their directory might or might not fit in the list at $5, depending on your perspective of the future. :)
There is still a bit of traffic in some categories...but not as great of a value as before, imho.
About the 'value' bit, use a tracking service / script / or something to monitor all your campaigns, tweak them over time.
As far as I've read here & by using the site search [webmasterworld.com] those seem to be the universal best bets for ROI.