One source recommends visiting the SemSim site where you can partake of exam simulation coupled with router simulation, geared especially for the CCNA exams. The 640-607 CCNA exam is now obsolete and the new version is called the 640-801 Exam for Certification in CCNA 3.0. If you prefer to stagger the subject matter, then you are probably thinking of taking the INTRO exam (called 641-821) and the Interconnecting Cisco Networking Devices (called 640-811) one after the other.
You may want to visit the website of Todd Lamle to take advantage of his combination simulator and study guide dubbed Virtual Lab Platinum Edition.
The 640-801 exam may have questions regarding Wireless Ethernet; Configuration plus Implementation of a VLAN (based on the IOS command set of the Catalyst 2950 series) inclusive of the DOT1Q; Switch configuration (also using that command set of the Catalyst 2950 series); EIGRP; Single Area OSPF; RIP-Version 2; and Classless Routing (with variable-length subnet masking included.)
People who have zero to little networking experience have the most to benefit from the formal studies offered by a local Cisco Networking Academy. They can also take advantage of publications from Cisco Press.
If you need the comfort provided by an online community, try going to CCPrep.com, which even offers preparation services for the CCNA exam.
If you want to be challenged by weightier study materials, then head for Examnotes.net. Take note of the Cisco router configuration offered here.
It also pays to constantly visit the official Cisco Systems website to see what new developments have come up lately.