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: 
If you have the money, go with the full frame option. The basic reasoning that I would have for that is simple: lenses will stay with you longer than the camera body. That's the nutshell answer.

Longer answer is that today you have a 550D and you're learning. Stay with that camera while you're doing that, until you feel that the photography you want to do is being impeded. Then you're going to look for something else. You might stay cropped sensor, you might not, but if you've shelled out thousands for lenses that are crop, then that may make the decision for you and that isn't ideal. Or you'll need to sell your lenses and you'll lose money in replacing. Also not ideal.

Net effect, if there is ever a real possibility that you'll buy a full frame Canon, new or used, then stick with the full-sized lenses. If this isn't a real possibility, then go crop. Just seriously consider all that first.
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.