Hi Robert,
GetListed.org is probably the best. It not only tells you which directories to get listed in, it also verifies when your business has been listed.
The directories on GetListed.org are great, then any other industry specific or local business directories you can get into will make complete sense to Google when crawling. It starts to become a sketchy area when you start adding your website to random or generic directories... some are OK, you just don't want to over do it in the generic ones.
Hope this helps.
Mike