Elegant and powerful
I have been using this library for 3 months, on a project where we were limited to Sharepoint Designer and clientside code.
I stumbled across this library when looking for problem fixes (for multi-select boxes and cascade filtering dropdowns). However the range of Utilities & web service calls available has meant that this has become my most-used Toolset.
This library has enabled us to build and release a 700 user forms-based site (including finding a workable solution for filtering a 5000 row look-up).
Many thanks to Marc and team for providing such a well-documented Codeplex toolset and for the amazing level of support.
SharePoint Designer-friendly tools
Can even be used if you only have a web browser + designer/site owner level access