Sometimes Bettas don't get along so great with the frogs, I've noticed. A few of my male Bettas have taken very mean nips at my frogs, but most of them haven't. My females, surprisingly, have never taken a single nip at the frogs.
I've never seen a single problem with housing Bettas with Cory Cats. Mine are Albino Cory Cats, but I don't think that would make a difference.
Some people say that Bettas get along famously with Mollies and Platies. I don't know about Platies, but my female got along fine with Mollies...it was one of the Mollies that didn't get along with her. I found her hiding in a corner with the Molly trying to nibble on her. Needless to say, she came out of that tank pretty quick.
Guppies are generally a bad choice for housing Bettas with. I have one male who doesn't mind Guppies at all, but my male Guppy considered the Betta a threat to HIS manhood, and took a little bitty Guppy-sized bite out of my Betta's tail. The Betta now no longer lives in that tank.
As for housing Bettas with Gouramis, I wouldn't really recommend it. That said, I'm currently doing it. Of course, I didn't know they were Gouramis when they went in that tank, but they are two Croaking Gouramis living with 5 female Bettas and 3 African Dwarf Frogs. However, it's very risky, and I watched them almost nonstop for days before I felt comfortable leaving them together.
Sometimes Bettas try to eat snails. The same goes for Ghost Shrimp. If you intend to put the species together, it's something you'll need to be aware of. In the case of snails, there have instances where the snail has closed its "trapdoor" (for lack of me knowing the real term), and the Betta's nose has been stuck in there. Hasn't happened to me. Probably only happens like a one in a million shot. But it's always something to be aware of.
White Cloud Mountain Minnows. Usually, as long as they aren't bite-size, the Betta doesn't mind them a bit. USUALLY. Each Betta is different, of course.
Zebra/Leopard Danios. If not kept in the proper numbers (6+), sometimes they nip. Many times kept with female Bettas as a dither fish, to keep the female Bettas from nipping on each other. This is because they zip back and forth all day long, and their activity distracts the female Bettas from their behavior. That's the theory behind it, anyway. This is a tricky pairing. Sometimes it works, sometimes it doesn't. Sometimes the Betta goes after the Danios, and sometimes they go after the Betta.