when and why did they redesign the nickel again?

Question

i have noticed another new design on the nickel, instead of the new one released a few years ago.

Answer 1

The first 2 design were in 2004
The 2004 Westward Journey Nickel Series™ Designs
2004 Spring Design: "Louisiana Purchase/Peace Medal"
2004 Fall Design: "Keelboat"
http://www.usmint.gov/mint_programs/index.cfm?action=NickelSeries2004

The next 2 were 2005
2005 Obverse Design: "President Jefferson with Handwritten Liberty" for both coins.

2005 Spring Reverse Design: "American Bison"
2005 Summer/Fall Reverse Design: "Ocean in view! O! The joy!"
http://www.usmint.gov/mint_programs/index.cfm?action=nickel_series

The 2006 is just 1
2006 Obverse Design: Jefferson, 1800
2006 Reverse Design: "Return to Monticello"
http://www.usmint.gov/mint_programs/nickel/index.cfm?action=returnToMonticello