1) Make sure your "Sponsors" header and "Design Showcase" header line up. As it is, the Sponsors header is just far too high, it puts the whole layout on tilt.
2) Main header image. Yikes. This screams "low quality" to me. You must have tons of vectors at your disposal and, hopefully, be a master yourself, but that’s all you can come up with? Get creative! Make a logo!
If I had to guess, it looks like you’ve bought a pretty decent template and then added the header yourself. It totally clashes, you need to make that better to get any respect from a designer who has stumbled upon your site.