I use a Sigma 10-20mm for my Pentax and it is by far my favorite lens in the bunch. Almost all the shots I took on a recent outing to Banff were taken with that lens.

I would suggest though that before you go out and start investing gads of $$$$ on lenses, that you first take the time to learn your DSLR camera if you are a beginner. You should have a basic decent lens that can shoot a bit of wide angle shots ..mine came with an 18-55mm kit lens which I still often use for wide angle shots...it is a good all around lens to learn from and I still often use it.

I think learning the nuances of the camera and how to expose and compose shots will get you far further in photography right now than any lens will. If you are new to the DSLR world learning the basics is far more valuable right now than spending more money on lenses.
I understand the passion and the enthusiasm and I am not trying to quell it but I know that what makes and excellent photography good is proper composition, exposure and detail and learning the techniques of how to do it.
That's how I did it anyway.
Just my