Cryptography is a complicated science that I don't personally feel qualified to make a specific recommendation about. For a good overview of different cryptographic techniques and algorithms, go get a copy of Applied Cryptography by Bruce Schneier. It's quite good, especially if you like books with source code included.
Now, let's think simpler: The real question here is how secure does your data have to be? If absolute security is a must, the don't send your data over the internet at all. Put it onto DATs and hire a courier to transport it for you. You might also want to consider a VPN, which will automatically encrypt all traffic over a network link. Your server must be secure also. If the attacker can get into the server and steal the unencrypted data, there is no point in encrypting it first.
Wrap up: Sorry that was so long a rambling. Remember, your server must be secure first. Think simple, but secure. Physically moving the medium is more secure than emailing or ftp'ing it. If your data is that important to you (credit card numbers, social security numbers, bank transactions), hire a professional who has experience in this field.