I used to quite like photosig. It is quite good if you want people to critique your photos. Comments tend to be quite helpful, although I sometimes felt that sometimes people were making a comment for the sake of making a comment (you get a score based on how much you comment). Be prepared to feel inadequate, there are some fantastic photos on there.
For something a bit less formal try flickr. There are groups for practially any type of photography you could name.
What type of photography are you into? My preference is for wildlife, unfortunatly much of the wildlife I shoot is behind bars.
If you do join flickr feel free to add me as a contact
http://www.flickr.com/photos/captain_chickenpants/
[edit] Some additional info, hints.
I assume you got the standard Kit lens? If so play around with it for a bit and try and figure out what kind of focal range you need, don't immediatley spend money on a big zoom lens if you don't actually have a need for one. When you do start buying lenses try and buy the best that you can afford. A good lens will last through several camera bodies and are more important for good images than a higher resolution sensor.
Where possible try and borrow a lens that you are considering buying so you can see how they feel and what the image quality is like.
I tend to shoot in RAW mode as it allows much flexibitilty when it comes to processing your image, images that look under/over exposed may be recoverable if you were shooting in raw.
CC