Just found this free ebook on the Red Gate site:
This book is for busy programmers who want a succinct and yet readable guide to C# 3.0 and LINQ. C# 3.0 Pocket Reference, written by Joseph and Ben Albahari, tells you exactly what you need to know, without long introductions or bloated samples. Boost your C# expertise and keep ahead of your peers! ->
Download it here: C# Pocket Reference Second Edition
UPDATE: Sorry, the pocket reference can not be downloaded from the Red Gate site anymore. But with a bit of smart googling, you might still find it.