Model objects linked directly to db tables?

[eluser]WanWizard[/eluser]
Lots.

You can either go for a lightweight MY_Model solution that your models can extend. Jamie Rumbelow created a good one.

If you're looking for more advanced features like for example relations (so you can easily fetch all groups related to a user for example), you need to look at an ORM.

Search here and you'll probably find a few...