It is a good idea to send a letter of thanks after an interview. If you need some help getting started, check out these web resources.

CareerLab - several sample job searching thank you letters, including letters for after an interview.

Professional Writing - help with professional writing of all types, including thank you letters.

Sample Thank You Letters - from Monster.com

Sample Thank You Letters - from Job Searching Technical @ About.com

Thank You Letters - several helpful resources from About.com Job Searching.