TrueCrypt is free and cross-platform: http://www.truecrypt.org/
If you're only on Mac, encrypted disk images are very easy to make and use: http://matthew.mceachen.us/blog/free-easy-encrypted-storage-...
The same problem happens with every encryption solution that uses a large container. The only viable solution is filesystem-based encryption schemes that work with individual files, like EncFS or eCryptFS.
By the way, SpiderOak has client-side encryption and two-factor authentication. But it's slow as molasses.
The bigger problem would be to access it e.g. on your iphone/from the web. For that reason, the webservice should be able to serve an unencrypted part if you enable that functionality. upon providing the passphrase, of course and waiting for the decryption. that could be a special feature which costs more, but would definitely add something special, which others do not provide as of now.