Hello,

I am working as a Force.com developer from last few years and now realizing that its very important for developers to get certified because many organizations and clients prefer certified developers.

When I was searching for the SalesForce certification related stuff for developers for me and my team I found following useful links. Might be useful for the others too

This is what I found, but its not complete. Provide more links and sample questions if you have.Thanks in advance

Lanading page for certifications

Look at the bottom of the page for the study guides for varios exam types and levels.
http://www.salesforce.com/services-training/training_certification/certification/ 

For developer certification

http://www.salesforce.com/services-training/training_certification/developer/

Video Trainings from SalesForce
Following link has video traings provided by SalesForce
http://www.salesforce.com/services-training/training_certification/online/

However SalesForce also offers premier training material but which is paid, One can apply for it by clicking a link given at the bottom of the above url page.

More Links

Following site offers you more material and guide lines for the certification related stuff for free.

http://forcecertified.com/certifications/

This give you detailed information about the overall schema for the developer examination levels
http://forcecertified.com/category/certified-developer/
http://forcecertified.com/category/certified-advanced-developer/

More Video training material
http://itunes.apple.com/WebObjects/MZStore.woa/wa/viewPodcast?id=325668840

Certification Blog
This also has some sample questions
http://mysalesforcecode.blogspot.com/2009/03/developer-401-forcecom-exam-tips.html

If you have more material or want to share any information or have any queris feel free to contact me @ rohit.marathe@trekbin.com