What do you intend to do with C - embedded stuff, general programming, programming PDAs, GUI applications, number crunching computations etc?
Pick an area you're interested in and then pick a book on C which covers that area. The ForDummies books are great for starting off but once you've started, they don't quite go far enough. Books like "The C Programming Language" and "The C Reference Manual" are great as references but quite low on examples and exercises.
Also, pick one that is suitable for your OS if there are any OS specific examples. For instance, if you are running Windows, don't pick a Unix book.
If you pick an area you're interested in, you can expand on it. It is difficult to expand on an obscure example on totally unrelated topics. For instance, if you wish to do hardware interfacing, learning the ins and outs of programming GUIs won't get you anywhere.