The 50mm 1.8 is good (great at it's price of $79)
The 85mm 1.8 is one of Canon's absolute best lenses at $300ish I believe
For event shooting you'll probably want a zoom... there are a lot of zoom lenses! If you need a good wide angle, the Tamron 17-50 f/2.8 is reviewed well, and the Tamron 28-75 f/2.8 is reviewed well too. Those are third party, but supposedly great lenses.
For shooting portraits, I prefer to shoot primes... unless the subjects are running around like children. My favorite focal lengths on my Canon was 24mm, 50mm, 85mm, and 135mm. On a budget, you can start with 50mm f1.8 (or f1.4) and/or the 85mm f1.8.
If a zoom is necessary, the 24-70 f2.8 is known as a staple for Canon Wedding photographers. Fast aperture, wonderful image quality. I found it a bit short on the focal range for the weight.
BTW... For portraits, the lighting is as important (even more important) than the lens. Be sure to put some thought into lighting if you want successful portraits.. whether you choose dedicated flash, reflectors, or full blown strobes.