LINQPad supports everything in C# 3.0 and Framework 3.5:
- LINQ to SQL
- LINQ to Objects
- LINQ to XML
LINQPad is also a great way to learn LINQ: it comes preloaded with 200 examples from my book, C# 3.0 in a Nutshell. There's no better way to experience the coolness of LINQ and functional programming.
And LINQPad is more than just a LINQ query tool: it's a code snippet IDE. Instantly execute any C# 3 or VB 9 expression or statement block!
Best of all, LINQPad is free and needs no installation: just download and run. The executable is only 2MB and is self-updating.