My gut feeling is that many of the directories out there are a waste of time and effort. Some might even be detrimental to be in, if google classifies them as junk or spammy sites.

I'm most interested in directories that can boost google pagerank or that can send significant, genuine traffic. Given this, please recommend directories that you feel really make a difference and are worth the effort.

Lastly--on a side note--I've seen mixed opinions about the value of business.com or the 'go guides.' Anybody feel strongly that they are worth paying to be listed in? And for what reason: PR or traffic, or both? Thanks!