When is the best time to find bugs in animal crossing?

Bugs like fish vary by month/season. While the largest selection of bugs are available from Jun-Sept there are fall/winter specific bugs as well.

This is a spreadsheet of basic info:

http://faqs.ign.com/articles/100/1005531p1.html

A comprehensive post elsewhere:

http://www.wiipals.net/Forum/f28/official-animal-crossing-city-folk-bug-fish-list-price-time-month-62889.html

Happy hunting!