I bought my first betta a couple days ago and got some neons at the same time. They all went in our 125 litre tank with 6 guppies. I knew it was risky but was hoping for the best... the guppies didnt seem to bother him and neither did the neons until the next day when I saw him swim up to a neon and attack him! The neon was ok afterwards but the next day I found him dead. I wouldnt risk it again, it could have easily been the guppy he swam up to and did that.
Alot of people say it depends on the bettas personality etc - and they are right. However my betta seemed perfect in there until this incident with the neon. He is now living alone in another tank. If I were you I wouldnt risk it, its lucky I saw him attack the neon otherwise I could of gone to bed and woke up with NO guppies and NO neon left!
I wouldnt if I were you
Some times you will be able to have bettas with other fish, often not though. Guppies are a no no, they have tails that can confuse the betta into thinking its another betta and so it will attack them, they also can be a little nippy when they want to be. Best tank mates in my view are cories and ottos
I find that Dwarf Aqautic frogs make great tank mates, I have one(Jack S.) with my Betta(oscar) there has never been any problems at all im not even sure if oscar knows jacks there