In a 10g, you could easily keep a betta and a couple of African Dwarf frogs as well as a few small and peaceful tetras such as neons or glowlights. I keep a betta in a 10g with pygmy cories, ADF's and some ghost shrimp (my betta doesnt bother the shrimp, but its heavily planted with a lot of hiding spaces). You can also keep a betta with harlequin rasboras. Maybe even 3 or 4 regular sized cories. Of course, I don't mean all of those together...you'd have to pick and choose.
This all is somewhat dependant on the attitude of your betta. Some tolerate many other fish and critters perfectly...others won't accept a snail being in their tank. It is kind of trial and error. So, if you do decide to add something, add it on a day when you can be home to monitor what happens - and have a backup plan (like taking the fish back the LFS) if it seems as though your betta is going to cause serious harm to them.