I would like to just give you couple of websites and blogs where you can get almost all wordpress plugins. I think this might be dumb for somebody that is good with wordpress, but believe me there is many people out there that does not even know how to install wordpress plugin.

So here are couple of very known wordpress plugins.

wp-plugins.net/ -great source of plugins if you are looking for something specific be short in search engine top right.

wordpress.org/extend/plugins/ - original wordpress site where else !

dev.wp-plugins.org - got some here too ! the only thing that I dislike is the navigation to it.

alexking.org - lots of old and new wordpress plugins.

lorelle.wordpress.com - couple of other wordpress plugins

Please provide links in comments for other wordpress plugins