Upload & Sell: Off
The T2i is a 1.6X crop camera, so multiply focal lengths by 1.6. So a 50mm lens has the same field of view on a T2i as an 80mm lens on a regular 35mm film or full frame digital camera.
80mm is a classic focal length for portrait photography. So I agree with those saying 50 f/1.4 *if* what your friend wants is a dedicated portrait lens.
To suggestions of 24-70, 28-80 or similar lenses I would say those zoom ranges are intended for full-frame camera, and are too long on a 1.6X crop body. The 18-50 kit lens, times 1.6, is almost precisely a 28-80! That is to say, the 18-50 is the crop "version" of the classic 28-80, or 24-70, or similar zoom for full-frame bodies.
What I *speculate* your friends would be happiest with, if what they want is a single lens of high quality and flexibility. is a greatly improved standard zoom for a crop camera. Their best bet, in my view, within a $350 budget, is a Tamron 17-50 f/2.8 zoom. It's a "fast" lens, meaning good in low light and also capable of nice background blur. It's optically of very good quality. And it has the highly flexible zoom range of 28-80 equivalent.
With this lens (buy it used from someone here on FM for $325 or $350) they'll see clear and immediate improvement in image results. And they won't be locked into a single focal length.
By the way, if they go this route they should sell the kit lens. They can probably get $60-100 or something like that for it, offsetting the cost of the upgrade to the Tamron f/2.8 zoom.