I have a whole freezer full of jalapenos - so yes, you definitely can.
They definitely retain their heat just fine.
They keep their texture better if you do 2 things:
Use a vacuum sealer and take out all the air - to reduce freezer burn. Because of this, I recommend you freeze them in batches.
Blanche them for 2-3 minutes in boiling water and then drop them in freezing water. From what I've read, this destroys a particular enzyme that helps not break the pepper down further. I've done this and not done this - and doing it definitely helps on the texture.
They should be good for a little over a year in a vacuum sealed bag - as far as the texture goes. They should never go bad otherwise.
Cos and Sobachatina - bring up another good point: freezing fast and effectively. You can try AB's method that Cos points out, but I do what Sobachatina does. Freeze on a single layer on a tray in the freezer. They freeze quicker and better than dumping them in a bag.