An effective and easy to use design. The only niggle I have is that the graphics are all a tad blurry - its like you've compressed them a bit too much. You can't fault the content though - its packed with good schtuff.
As for improvements... I've never liked designs that have large areas of null unused space. i.e. the right area on your design. Try adding a border on the right that marks the end of the site and a transition into some sort of funky background. For an example have a peek at
http://www.templatemonster.com/show....type=1&cat=All - although you can do it with a bit more pizazz than this fella. The grey is kinda boring...
