Question: I have a Canon 550D which I've been using for around a year now. I really love it and have learned a great deal with this and the 18 - 135mm kit lens. But now with experience I feel the need to get some better glass. I won't be buying a new body any time soon because I figure investing in some good glass is more important. 

As I have looked around, I see quite a few good used L lenses I can get in ebay for good bargain prices. But I know that the EF lenses don't have the same focal length in the cropped sensors. Is it a wise decision to buy these EF lenses or buy the cropped sensor alternatives?

I have the following lenses in mind that I am looking to buy down the line from the canon range over the next several months.

16-35mm f/2.8L, 24-70mm f/2.8L, 70-200 f/4L.

Are these apt choices for cropped sensors? I know most pros with FFs use these but I am a bit skeptic that they will serve the same purpose for me. If so what are the alternatives for this that have almost as good image quality?

Answer: 
The lineup of Canon crop (EF-S) lenses is not nearly as broad as the full-frame (EF) lenses.

* In the focal length of interest, some EF options give better image quality than the respective EF-S options.
* Additionally, some EF lenses offer features that are not available for EF-S lenses, such as weather sealing and stronger construction.
* (Not specific to the lenses you listed but) specialty lenses are only available in EF format, like fisheye and tilt-shift.

so yes, there are reasons to get full-frame lenses for a crop camera. For the specific lenses in question, @Joanne C's reasoning makes sense but today I personally think it is less important than it seemed to be in the past, as you have greater chances of upgrading your rebel to a higher crop body (7D class) than to a FF class. By the time you finally upgrade to FF class, you can sell your crop lenses for a good value.
Short form: 

In general it is wise then, and only then, when you seriously consider moving to a full frame body later. 

If you don't then it is just a case-by-case decistion, as yours obviously is. You are thinking of a number of specific lens for now. 
Then, when the choice is just beween an EF lens and an EF-S consider the following: 

* There is noting wrong with using an EF lens on a crop body. Nor is there anything wrong with a lens park made of both kinds.
* A crop body would use the best parts of the projected image only. Important when you take reviews into account. You can then ignore their less than optimal quality in the edges, that some of them may show.
* EF-S lenses of the same optical quality when used on crop bodies can be significantly cheaper than the EF lense that you compare it with.