Use Drip.exe / IEleak, I used it a lot to search for memory leaks!
Other hits:
- jQuery itself prevents a lot of memory leaks!
- Test your code with http://jslint.com
- There is a tool by Microsoft itself, but I don't know it is up to date: http://blogs.msdn.com/b/askie/archive/2008/12/31/javascript-memory-leak-detector-for-internet-explorer.aspx
- There is also integration with Visual Studio: http://berniesumption.com/software/how-to-debug-javascript-in-internet-explorer/
- There is a good article about mem leaks http://www.ibm.com/developerworks/web/library/wa-memleak/
- http://www.debugbar.com/?langage=en