I have a Canon T2I, and also a good prime lens (50mm / f1.8) but I cannot seem to take close up portraits like I see in magazines. Do I need a better lens?
Well, a classic lens for portrait is 80mm to 135mm on a 35mm full frame camera. If you do the math, on the 2Ti it's around 50mm to 85mm for the same field of view. So, in that sense, you're at the wide end of the portrait "sweet spot" as it were.
Does that mean anything? Well, it does. A shorter lens will often have a greater depth of field and that tends to bring backgrounds into focus and that adds distraction to the primary subject. Also, the smaller the sensor, the greater the depth of field. So, for a dSLR, I'd recommend getting to farther end of the range for the APS-C (70-85mm) to get that nice bokeh on the background that makes the subject pop.
Now, having said all that, it is important to realize that magazine shots have a few other things going for them such as:
Very experienced portrait photographers. This shows in their manipulation of light, the angle of the shot, and the depth of field they aim for.
Very experience makeup artists. You can't discount this, high end work isn't just the camera and the lens, it's also the people behind the scenes that make sure everything is perfect.
Top of the line post-processing. If you have ever seen the photo manipulation done during the work for a professional magazine shoot, you'd get over the limitations of your own efforts. This level is insane, they will adjust anything at all to make the shot look better. Sure, they have to start with something, but after they're done, it can be night and day.
Anyways, to get good portrait shots it is a balance of the right lenses, as I mentioned, and the right light. The right light is a whole new level of challenge and there are some great sites to help you get started:
Good luck! In the end, to get the great shots takes practice, so dig around these sites and shoot.
What flash unit(s) have you got, if any? A good flash with bounce capabilities, or better still one or more off-camera flashes can do a lot for your portraits. Photos in magazines will almost always be shot with multiple lights, so maybe its not a lens you want so much as a with bounce capability (Canon Speedlites 430 or 580), and maybe a remote trigger to get it off the camera.
I'm going to give you the kind of answer that doesn't fly too well around here: outside of the MP-E, any lens Canon makes is a good lens to take portraits. I've seen great portraits shot with super wide angles, I've seen them shot with super-teles. Personally, I love shooting portraits with a 28mm lens and would recommend that focal length to anyone interested in people photography.
A wider lens allows you to put yourself "into" the situation - you're not offering your viewer a peephole into your world, you're taking them along. You photograph people with context - something so many amateur portait shooters forget. Closeups of faces are trite and boring, there's no story in them no matter how weathered the features. Back up a little and you open a whole world, and that's pretty cool.
Like John Cavan mentioned you are on the short end of the classic 80-135mm effective focal length range. While the 50mm is a great lens, if you're wanting to get the really close shots you might want to look at the 85mm f/1.8 USM. That would put you on the other end at an effective length of 136mm. The longer length will help compress the image a bit so you won't see as much depth in the subjects face, which is generally more appealing.
I personally use my 100mm f/2.8 USM Macro with a Canon Xsi, which with the sensor crop is a little long, but it is a very sharp lens, and I have been really pleased with the result. The macro lens is a little slow to focus, but for portraits that hasn't been much of an issue.
135/2 is an excellent value and extremely flattering lens, but requires that you move around your subject since it is a prime
70-200/2.8 is very flexible, and gives you a chance for quick candids by zooming in
50/1.4 is great for intimate shots (/1.2 is poor value)
85/1.2 is a boutique lens - make sure you know that you need it before dropping money on it - the 135/2 is a much better value. The 85/1.8 is solid, but I prefer the flatter perspective of the 135/2.
Some people like macros for their sharpness (sigma 150/2.8 or canon 180/3.5) but with portraits you don't really want extreme sharpness, as much as more pleasant bokeh