Propel ORM?

[eluser]Rick Jolly[/eluser]
Other ORMs:

Doctrine http://www.phpdoctrine.net/trac/
The new kid. It is built on PHP 5 PDO so it should be the fastest ORM. No seperate schema file required. It defines data types and table relationships in methods within the model.

EZPDO http://www.ezpdo.net/
Innovative because it uses comments in the models to determine data types and table relationships. Therefore, like Doctrine (and unlike Propel and DB_DataObject), there is no seperate schema file to maintain. However, it is probably the slowest ORM.

Pear DB_DataObject http://pear.php.net/package/DB_DataObject/
PHP 4 and maybe the easiest to use. It makes the simple things simple and the more difficult things (joins) possible. Not a full-blown ORM. Can be used without a schema file for determining datatypes, but that requires first querying the database for metadata which is slow.

As for integrating any of these into CI. That's fairly straightforward: just set the include path and require() or include() them.