Is D3100 a best entry level DSLR camera?

I'm an entry level photographer and planning to buy Nikon D3100, please suggest if any other camera model with the better features exists for the same price.

Please let me know whether Sigma or Tamron lens are good for D3100 and also suggest me a better low budget lens for D3100.

That's basically an entry level camera with video capabilities. So its perfect for beginners.
The lenses depend on what you like to shoot. In my opinioin, Sigma is a little more expensive but has better build quality. Tamron is cheaper but not quite built as solid. But I've read reviews that both image quality is still fairly good for the price.
On a DX camera, I feel the 35mm 1.8 is a must have. You should look into getting one of those.

D3100 is a very interesting choice for a beginner. Put a nikon 18-105 on it and you've got a nice and versatile combination

Pentax K-x, TIPA's best entry-level dSLR for 2010.