128 bits is still strong and will be for the forseeable future, excepting a sudden mathmatical breakthrough. Further, the cost to brute force rises exponentially with the keysize and can easily outpace Moore's Law.

You would do well to pick up a copy of "Applied Cryptography" (or "Practical Cryptography", which is sort of the updated version, but I haven't read it myself yet). In particular, you may find the chapter on combining ciphers enlightening. You can't just put two 256-bit ciphers together and get a 512-bit cipher. IIRC, you're not worse off (security-wise) than if you had only used one cipher, but you're probably no better off, either. It's possible to combine ciphers, but it has to be done carefuly.