Few great Visual Studio 2010 extensions (many of them are part of Visual Studio 2012) :
NuGet -> Manages 3rd Parties libraries and preferences
Web Essentials -> Code Collapsing, add vendor specific css properties, much more
Web Statndards Update -> HTML intellisense and validation
WoVs Default Browser Swithcer -> Quickly change the default browser from Visual studio
JSLint -> Javascript Code Analysis
CSSCop -> Catches common javascript issues
Resharper 6 -> Javascript refactoring tool (This is a paid one)
----- Any other suggestion Guys
