Niche specific directories are the way forward!
I just wanted to say that there's a huge number of directories and search engines out there that are specific to a particular niche, which can be very fruitful.
Too often, I think people don't look any further than Google, DMOZ, MSN, AV, etc. But really, it's the directories and SE's that are specific to your niche that can bring you the most (quality) traffic.
Have a look around - you'll be surprised how much is out there. Try searches on Google for things like:
<your niche> search engine
<your niche> directory
<your niche> add url
<your niche> submit
<your niche> etc.