I've heard that if you provide a link from your repo to some web page (blog, project web or similar), that other page will have its rank increased. And if that other page contains a good description of something people are looking for (as well as a link back to the repo), they are bound to find your repo that way.
Personally I've never used a specific site to find stuff. If I need something done and believe there are finished scripts/projects to handle it, I just google. But bear in mind that not only descriptions are crucial for this, but also naming. I remember not finding anything that would turn wsdl documents into php proxy classes - until Weedpacket pointed out that they would commonly be called wsdl2php… Then I got more than enough hits.
I would also recommend including a readme file in the top level directory. If people are able to quickly determine if your code does what they want and also quickly estimate how much time, effort and knowledge will be required to use it, you are more likely to get happy users who in turn spread the word and more importantly repost the link.
