NSIS-Toolbox is a project mainly written in ..., it's free.
A collection of collected and developed scripts to make NSIS development easier
A library of utility macros (and perhaps functions) to ease development NSIS scripts.
Future Goals: An NSIS guide for newbies to help level the VERY step learning curve. Making NSIS do what you want is easy. Writing it in a maintanable and extendable way is hard!