Since most summary has been mentioned, I'll throw in my 2 cents.
I have a D3100 and I love it. It's a beginner, crop sensor but with decent lens it can really throw out some great shots.
I have a 35mm f/1.8, kit lens (18-55) and a 55-200 f/4-5.6
I'm in love with my prime lens, and plan on picking up a 50mm f/1.8. Both can be had around $200 each, they cheapest lens that produce amazing results.
The D5100 has a higher ISO range than the D3100, but if you're doing landscape I'll assume you'll use a tripod anyways so that really shouldn't matter.
Here are some shots with the 35mm. Even though it's one of the cheapest cameras out there, it puts out nice shots:
http://farm8.staticflickr.com/7145/6608749271_f741c47d38_b.jpg
Crack one open by M0nk3yy31, on Flickr
http://farm8.staticflickr.com/7002/6614084239_9b04a18446_b.jpg
Reflections v.2 by M0nk3yy31, on Flickr
http://farm8.staticflickr.com/7063/6799315846_4579f410fd_b.jpg
Evo Engine by M0nk3yy31, on Flickr
http://farm8.staticflickr.com/7208/6970174475_fab8eba5c8_b.jpg
Thinking About Golf by M0nk3yy31, on Flickr
A kit lens shot:
http://farm8.staticflickr.com/7008/6420399133_317614ddd4_b.jpg
Into the Unknown b/w by M0nk3yy31, on Flickr
And a 55-200 shot:
http://farm8.staticflickr.com/7171/6608306863_ce047cf139_b.jpg
Maverick by M0nk3yy31, on Flickr
Best of luck