Oh man, this is totally my thread. List of bands to check out:
The Softies
The Moldy Peaches (Hello, "Anyone Else But You.")
Belle & Sebastian
Beirut
Iron & Wine (Sam Beam does a cover of "Such Great Heights," as a matter of fact.)
Jens Lekman
Kings of Convenience (Don't quote me on this one, but they do some cute songs.)
Shout Out Louds
Wilco do some really adorable songs, too.
Ray LaMontagne
There are a handful of bands that sound "cute," but I'm not sure all of their songs are necessarily about love.