web2py gets a lot of hate from some parts of the python community (with Ronacher & Moss-Kaplan being the most prominent examples), but its DAL (Database Abstraction Layer) feels like the right way to approach this: It's not an ORM, but it gives you a lot of what ORM gives you; It's not directly SQL, but the mapping between DAL code and underlying SQL is almost trivial (though it might depend on the specific DB). It just works well, and can be used independently of web2py.

It will even do database migrations for you if the schema evolution is reasonably simple.