I like CGI::Cache, since it can help people get massive speedups on CGI operations, and is dead simple to use.
Benchmark::Timer is better than Benchmark because it will automatically figure out how long to run the code until the execution time is accurately measured.
Module::Install is pretty awesome, if nothing else than because it provides a modular way to encapsulate common Makefile.PL code. (e.g. like Module::Install::GetProgramLocations for having the user provide paths to dependent applications on the system.)
