Over on my other website - http://www.happyslob.com - I write a lot about using baking soda and vinegar together to clean. But, I've found a new set of favorites too -- using vinegar (or lemon juice) and plain old table salt.
The vinegar is very acidic, and the table salt helps add some grit to the mixture. This is a great mixture to use to scrub the bathtub or shower, or sinks...anywhere you need a scrubby mixture to really clean surfaces. Enjoy!