SharePoint 2010 Sandboxed Solutions - Solution Validator.
This is a start up template and you can extend it as you want. This is a working tested code with out any rules. You can add your own rules while validating the same.
In the next ( beta ) release I will add more rules on it.
You can also find more details on my blog post mentioned below.
http://codename-srini.blogspot.com/2010/01/sharepoint-2010-sandboxed-solutions.html