To continue in the spirit of free products, Apress.com is giving away digital downloads of The Definitive Guide to Linux Network Programming.
The book has a list price of $49.99, and is available for free download here.
Update: the download link appears to be down on Apress right now (due to massive traffic). Here is a temporary download link.
For those of you who don’t like staring at computer screens too long, you can purchase a hard copy on Amazon for $35 (Amazon link). It has pretty good reviews on Amazon so far, so this 400-page book is certainly worth adding to your arsenal.