As you are a java developer so you dont need to start from Head First, you can straight with good SCJP book(you can go for Khalid Mudhgal book also).Later on you can practice from Mocks available free and commercially.Anyway you can find all of the info in this Javaranch Forum itself. This link may help you all you need -: Click Here
I'm not afraid to say that the best SCJP's book it's SCJP Sun Certified Programmer for Java 5 Study Guide For Exam 310-055, by Katherine Sierra and Bert Bates. It's a kind of a bible of this certification.
Elton Kuzniewski<br>SCJA 1.0, SCJP 5.0, SCWCD 5.0, SCBCD 5.0, SCJD (B&S - working on project),
<br><a href="http://www.eltonk.com.br/" target="_blank" rel="nofollow">www.eltonk.com.br</a>
To begin with kathy sierra and Bert bates is very good... and once you are finished with this problems in khalid mughal will be very helpful... but kathy sierra and bert bates itself will help in a major way....