Web directories are coming up everywhere these days and are useful for building traffic and a higher Google page ranking. I've joined many directories that have come and gone over the years, in fact I recently had to join a new bunch again to improve my page ranking because the ones I had joined a couple of years ago turned belly up.
An easy to use SEO friendly web directory is easy to find over the place now I joined a load (most of them I've linked to in the sidebar) and my page ranking has gone from 0 Google to 2 which isn't so bad in such a short space of time.
Directories are not just for increasing your page rank though they also advertise your business if you have one “Best On The web” has been around over 10 years and is still going so they are worth listing with as they aren't going to go under (hopefully not anyway in this financial crisis). If you are strapped for cash then you could always try a free web directory, you probably won't get as prominent an ad unless you upgrade but it's a start and all back links improve your page ranking in the end so it's still worth it.