During a recent project I ended up using ADODB and found it very effective. Especially the wrapper it places around PHPs sessions, it stores them in the DB instead of in the temp directory, which can be less secure. It also handles encryption of the session variables contents, but only using MD5 originally and I prefer to use SHA1. So I hacked the following to allow me to do so and I contributed it to ADODB.

adodb-encrypt-sha1.php (new file):

http://gist.github.com/294724

Add to crypt.inc.php:

http://gist.github.com/294725

This code has now been added to the stable release of ADODB.