"If you need to perform data analysis, provide graphics for your users in your webapp, or produce high quality plots I encourage you to investigate the combination of ruby, GSL and GNUPlot." Looks good. I should probably give this a poke some time; could come in handy.

"Faker, a port of Data::Faker from Perl, is used to easily generate fake data: names, addresses, phone numbers, etc."

Geokit is a Rails plugin for building location-based apps. It provides geocoding, location finders, and distance calculation in one cohesive package.