A set of links that I'm posting because 1) I don't want to lose them and 2) they're handy for people to read.

1. Reusable IQueryable base classes
2. Where and reusable Expression tree visitor
3. Local variable references
4. Select
5. Improved Column binding
6. Nested queries
7. Join and SelectMany
8. OrderBy
9. Removing redundant subqueries
10. GroupBy and Aggregates
11. More of everything
12. Relationships and the IQ Toolkit
13. Updates and Batch Processing
14. Mapping and Providers
15. Transactions, Sessions and Factories

The source code found in this series is also available at CodePlex.
http://www.codeplex.com/IQToolkit