I am an IT Consultant working for 10 years,7 years in U.S.
I worked for major fortune 500 companies like AT&T, AOL, COMED, DUKE ENERGY, EDS.
I worked twice for Fairisaac.
I rolled off recently from a short term assignment.
Here are some of my Tips to Roll off graciously:
1.Finish off all your assignments.
2.If you think,if you can't be able to make it within 5pm on the last day,inform your supervisor well ahead.
3.Send a thank you mail to the entire team you worked with.
4.If your supervisor or team members are free in the last day,go for a team lunch.
5.Ask their permission to give their contact details for further reference.
6.Collect their business cards.
7.If you have a Linked-in(http://www.linkedin.com) a/c,ask for a Testimonial.
8.Hand over the laptop or other materials,remote access key,badge to the right person.
9.Cleanup your working space before you exit.
10.Clean up your computer if you stored any personal files.
After the Roll off,keep in touch with them,you never know,you may be called in again.
I got the opportunity twice so far with the same client based on good referral.
Hope these tips are useful.
All the best in your job search!