There are many, many lists of WordPress plugins on the internet. I myself have previsouly linked to two of those (a more general and a more specific one). Here I go again: Best of: WordPress plugins from KylesCove.com. This one is quite long and is divided into several categories. Another one? Lorelle’s WordPress Plugins Series contains almost everything a WP user should know about. And if you still want more, you may leave a comment on Keith’s post New Plugin Ideas for WordPress and see if your suggestions will be taken.