build a 3D printer (posted fall 2009)
Extreme Wheelchair Sports (posted fal 2007)
Engineers Without Boarders (posted fall 2007)

Many of these competitions have significant financial rewards for winning. All of them provide an excellent opportunity to develop your engineering skills (technical, project, communication, etc.).

ASME Competitions. Some ASME competitions (for example Old Guard Oral competition, poster competition) are not specific projects, rather they provide an opportunitey for student to present their own work (such as senior projects) - these are excellent opportunities to develop communication skill. Some ASME competitions are specific projects such as the human powered vehicle competition.
 http://www.asme.org/students/competitions/

SAE Competitions (baja, aero, supermileage, etc):  http://www.sae.org/students/student.htm

ASHRAE Competitions: http://www.ashrae.org/students/page/1852

Alternative Power Initiative (competition with $ rewards) (posted fall 2010)

Association for Unmanned Vehicle Systems, International (several competitions of autonomous vehicles)

Institute for affordable transportation competitions: http://www.drivebuv.org/foundation.htm

Past U of P Senior Projects: (past final reports)
2005 Projects
2006 Projects
2007 Projects
2008 Projects
2009 Projects
2010 Projects