I'm planning to do my DEV 401 for the first time as soon as possible and I need to know the deadline for the Spring 14'. Also i'm bit stuck finding the updates for this release. It'll be a great help to know what should be covered, any resources for the spring 14' before taking the exam.
The Spring '14 maintenance deadline is October 31, 2014 - if that is what you mean?
You can always find the deadlines on the certification website here.
Salesforce recommend at the very least for this exam you watch the training videos on force.com, analytics and mobile which you can find here.
Don't forget you get three attempts at the maintenance exams, and it will ask a mixture of new feature material (from the videos) and standard platform questions to make sure you are properly in the loop.
If you just mean you are planning on taking the force.com certified developer exam, you will have missed the opportunity to take it as a Spring'14 developer (Exam code SP14) and you will have to accept that it's possible for you now to get questions for Summer'14 (SU14). To be honest, the scale of that difference will not be massive, you are pretty much either able to pass the certified exam or not! Watching the release material for Summer'14 would be useful if you are heading into that exam though. That is also on the training website linked about (just poison the URL to summer14)
I have given a presentation at Developer User Groups on the topic of getting certified, which you can find on my blog here:
Your core resource (As mentioned in my comment) for the certification exam is the fundamentals book though