Here's my 2 cents:
This is a good source with some nice directories
Other than that you could consider some other promotional methods like the following:
#1 Find what the most targeted keyword in your niche is. Build a page on your site which is dedicated to the keyword in question. The next thing for you is to start promoting this page like CRAZY. Hopefully this will help you rank higher in Google for this keyword. Let's not forget the social bookmarking sites. Submit the already built page to several Social bookmarking sites and don't forget to use the keyword as your tag in the description. You could also submit this page to some directories.
#2 Craigslist is a free classified site that can help you to promote your site as they get like several thousands of visitors per day. If done properly you could 'steal' some traffic from there as well.
#3 Posting and participating in forums that have relative to your niche information is a MUST! The posts should definitely be on topic and helpful to the community as your goal here is to have your site's link in your signature. Don't rush things in the first place. Wait till you have like hundred posts and only after that it could be okay to have your URL in the sig. Otherwise it could be treated as a way of spamming the community.
#4 Sites like WetPaint Wiki, HubPages, Squidoo are a good tool to create a subtle pages that have helpful information on the topic that your site covers. You can link them altogether and don't forget to link back to your site.
#5 Commenting on Blogs that cover the same topic is an essential part of the promotion. Post quality and though provoking posts, contribute to the discussion and don't forget to post your site's link.
Well, that's it for now! Hope it helps you!