Next portrait lens after nifty-fifty on T2i

[fstr]

I'd go for the new 40mm STM f/2.8 pancake.

In fact I have the 35mm f/2 and I want to sell it and buy the 40mm.

Although if by portraits you mean head-shots, you should really go longer, 85mm-135mm.

I get that people are excited about the new 40mm, but I'm not sure it fits the bill for what I'm looking for - portraits with DOF & Bokeh. That said though I may pick one up from the bestBuy across the street from work and give it a spin this weekend.
Also - 85-135mm on a crop sensor - I would need some serious elbow room! I would love for somebody to tell me 85mm will work as I think it is exactly what I'm looking for, just the wrong focal length. The 50 give me the ability to move closer for headshots and further for full body or group shots

[Dr Croubie]

I would love for somebody to tell me 85mm will work as I think it is exactly what I'm looking for, just the wrong focal length.

"The 85mm is exactly what you're looking for"

Better?

Seriously, it's a good lens. I've got the 40/2.8, 50/1.8 II, the 85/1.8, the 100/2.0. (and a lot of others, but they're my only 'autofocus primes').

Out of them I'd rate the 50 as the worst. Soft wide open, slow AF, crappy build (it's actually not that bad a lens, especially considering the price, but the other 3 are just way better).

The 85 and 100 are both twins, nothing different between them except the length. Focus is quick enough (i got the Canon 85 specifically for kids running around instead of getting the samyang or zeiss 85/1.4, then got the 100 a bit later because it was a bargain). Great IQ, you can shoot wide-open all day, stopping-down doesn't make it much sharper (you can't get much sharper), only increases the DOF (and wide open they have nice circular bokeh, stop down and it gets pointy).

The 40 i picked up on a whim when I went to buy film and I saw one on a shelf (the day after it was announced), I just bought it because I was happy Australia got it before the rest of the world. The focussing is fast enough, i'd rate it faster than the 50, and almost as fast as the 85/100. The IQ and Bokeh are both stunning, as good as the 85/100 (the bokeh of the 40 stays good when you stop down, although it's harder to get any because it's a wider lens). Only problem is that it's only f/2.8 (if you call that a problem). So you won't get that nice 'thin dof' look as easily as with a longer/faster lens, but that can work in your favour if things are running towards you too fast, there's more chance they'll be in focus at all.

So, what to get? The 85 (and moreso the 100), you're getting more and more into head-shot only territory. I've shot full-body (frame size maybe 1.5x2.5m) portraits, from across a medium-sized (50-100 people, maybe 10m away) room at a mate's engagement party. I've shot head-only shots from 2-4m away. I've shot full-body portraits of kids with them from closer, but then that's a 3-year old kid (frame size 0.4*0.6m or so).
I've taken group shots at a party with the 40mm on FF, I haven't played around with it too much but i've taken my 35mm Samyang (almost the same framing) to that engagement party and shot anything from single full-body from close, to small-group shots (just), on Crop.

It will all depend on what you want, really (and I know you'd rather have both, but you have to pick one). You won't be disappointed with any of the 3, choose more based on usage. The 85/100s are both available 2nd hand for $300-400ish, if you don't like it and it's in decent nick you could try re-sell and you'd probably get most of your money back. The 40mm is too new to find 2nd hand, but you can get it new for half the price of the 85/100s ($200 or so)