The only reason there's term limits on the president and not on Congress is that Congress would have to create its own limits. For senators and congressman reelection rates are so high (incumbents are reelected 95% of the time, and incumbents with six years experience are reelected 99% of the time) that a single election victory often acts as a lifetime appointment. Term limits would:
A) Decrease corruption
B) Make elections more competitive
All of these facts are proven by studies of states with term limits in their legislatures. Plus, a gallup poll revealed that 80% of Americans favor term limits.