A good rule of thumb is that if it's been around for a while, if it's relatively popular, and the code is open source, it's pretty damn tricky to put a back door in there.
When the NSA corrupted the RSA encryption, it wasn't a flaw in the encryption algorithm at all, it was in the random number generator. To the best of my knowledge, the RSA algorithm is still cryptographically sound, though clearly RSA, the company, can't be trusted at all.