There are many good tutorials available on the internet but after being through a few of them I have following to recommend.

For absolute beginners, Chris Brown’s four part series is an excellent introduction. The articles are rather short and deliver the concepts very nicely with lots of colorful figures.

With that under the belt, Advanced Linux Programming is the next book to read. The book is about 300 pages and does a rather neat job of exposing to the various system concepts accompanied with practical examples. The best thing is that it is free to download.

Another excellent resource would be the list of tutorials at the Little Unix Programmers Group. This has loads and loads of useful stuff.