The 35mm f/1.8 is an excellent lens, you should have no problem using it. It gives you an equivalent of 50mm, which is the perfect focal-length for everyday shots. It's a sharp, fast lens that you can't go wrong with!
Of course, there's also something like the 50mm f/1.8 AF, but you'll be left to manualfocus. There's also the 50mm f/1.4 AF-S, which will autofocus on a D3100. It's a bit faster than th 35mm f/1.8, which can be a huge benefit in low-light where you don't want to use flash. You can't however expect extremely sharp results at those apertures though.
Gear: 7 Nikon Nikkor AI-S and AF-S lenses, SB-700 flash, Nikon D7000, Nikon FM, variety of accessories
"There are no rules for good photographs, there are only good photographs."
- Ansel Adams