Here's a pretty encyclopedic overview of shelters. It should get you pretty well up to speed on what's available. It doesn't include a number of interesting models that came out in the past year (especially the Tarptent Stratospire 2, a double wall model that just came out), but it's still a good way to educate yourself on shelters.

I would frankly suggest borrowing or renting a tent to start with. This might give you a better idea of what you want--or don't want!

With any tent, you definitely want to set it up and put everyone inside before deciding if it's a keeper. Some two person tents are really too small for two people, and the 3-person version may be about right for two. Read carefully the specifications on the tent's website. With those in hand, you should be able to model the tent on your living room floor with masking tape and string. (Not my idea but Franco's--I've used his method several times, though, since he came up with the concept.)