See Also: Rijndael Members
System.Object
System.Security.Cryptography.SymmetricAlgorithm
System.Security.Cryptography.Rijndael
To be compatible with AES you should only use 128 bits as the block size. Other block size (192, 256) aren't part of the AES specification and may be problematic for interoperability with other implementations.
The AES specification is known as NIST FIPS PUB 197: Advanced Encryption Standard available at http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf
Namespace: System.Security.Cryptography
Assembly: mscorlib (in mscorlib.dll)
Assembly Versions: 1.0.5000.0, 2.0.0.0