Which SLR camera should a buy?

I really need a new camera. I don't want to get a little portable digital camera. I really want to get a SLR camera. I'm new to these types of cameras and I'm not 100% sure where to start looking. I went to a shop the other day and a guy there suggested the Nikon D3100? I was watching some test video's an YouTube and the quality is really good!
As long as the picture quality is 'crisp' and is can record a good quality video I'm happy. I just don't know where to start/ what to look for.
If you could please help me out that'd be amazing!

The Nikon D3100 is an excellent entry level dSLR

Whether the photos are crisp depends upon your skills using it.

That is a good basic camera. If you can, go to a store and ask to see one. Hold it, look at the features… > just see how it fits in your hand. Try a couple of others and read up on them. Then buy what YOU like best.
PS I own and like using a Nikon so maybe I'm a bit prejudiced on make of camera, but any camera will take good pictures IF the camera operator uses it properly. I learn more from my mistakes than the "good" pictures I take.
Have fun, its a life long journey!

If video is important to you then the Panasonic GH2 is the only interchangeable lens camera where video is it's primary function, capable of recording broadcast quality video out of the box, and cinema quality when hacked, but it's not a beginners camera. Video is a lot more technical than stills photography and takes a while to learn.

I have a D3100, and I'm very unhappy with it's video ability. Don't buy one for video.
The pictures are crisp, just make sure to use a decent amount of in-camera sharpening and auto-focus. Keep the ISO down… And use continuous mode so you can pick the "most crisp" photo.
Again, DO NOT buy this if your primary use is video. I find it hard to believe but I've heard there are DSLR's out there that are good for video. Get one of those. The D3100 is the basic bread and butter DSLR. It doesn't have a flip and swivel LCD(great for movies) and it doesn't even have exposure/focus bracketting(what is that all about?)
But I'm quite happy with mine, mainly because I'm familiar with the manual controls, know how to set the picture settings for in-camera JPEG processing, and most importantly, NEVER use it for video except short clips of me talking that I truly don't care about the quality of.