Best digital camera for beginners?

I own a Nikon D90 and want a better camera so my photos look better. I was thinking of getting the Nikon D800 or the D4. The D800 I'm sure will look better because of the higher megapixels which means its a professional camera. All my photos I upload to face book look blurry and blocky. Also The D800 uses the SD cards which my D90 does but also has a CF card slot, which I assume holds better quality photos since its bigger? I'd like to stay with Nikon because I have the 18-200 lens that came with my D90. But If I have to go to another brand like canon or hasselblad to get better pics then I have to.

Wrong. If you can't get good photos with a D90, you're not going to get good photos even with a Hasselblad HD4!
Wrong again, higher MP aren't going to help you. The Nikon D40 is only 6.1 MP, and I've seen pro quality photos taken with it.
If your photos look " blurry & blocky ", it's you, not the D90.
Not meaning to sound rude, but what you need to do is to learn how to use the camera that you already own. The D90 is considered an upper level semi- pro camera.
My advice? Buy a copy of "The Nikon D90 for Dummies " book. This is an excellent series of books. I've bought several myself.
FYI, Hasselblads are for people who know what they're doing.

If you can't take excellent pics with a D90 there's a fault with either the operator(you)or the camera. Just assuming that a CF card holds better quality images than a SD card tells me you have MUCH to learn about photography. I would mount the camera on a tripod, set the timer and let it snap a pic without ANY chance of camera shake. If it's good you know where the problem lies, it's operator error. If it's bad you need to get out the manual and start searching. Do you have a VR lens? Is the VR on or off? What resolution is the camera set to? The list is endless.

I'm pretty sure not just anybody out there can buy a Hasselblad camera since they are made for professionals and I think you need to be a licensed photographer to buy one, even used.