The Canon EF 50mm f/1.8 II is a $99 lens that's great for shooting photos and videos with. It gives you a very shallow depth of field and also makes it possible to shoot under low light conditions. It has a focal lenght of 50mm which equals 80mm on the 550D (crop factor 1.6).
Yes, most of the lens is made of plastic - but I don't care because the price is really good. One advantage is that it's very lightweight, but on the other hand you will hear some ugly noises (same as on the 18-55 kit lens) in your videos when you focus manually. But with an external microphone this problem should be solved. Autofocus is very fast and works great under low light conditions. But be aware that this lens has no image stabilization. So running around and shooting videos will not give you the best results (to avoid shaky images say Hi to a Steadicam).
What's really poor is that the lens hood for this lens (ES-62) costs $30. 1.8 lens - $99. Some plastic with Canon written on it - $30. This is a price I really didn't want to pay. So I ordered a $5 lens hood from China. And I think it's basically the same as the Canon lens hood. So here you can save $25.
The lens is really fast and it's much fun to shoot videos with it since you can turn down the ISO values when shooting under low light conditions which will avoid ugly noise. This lens + hood combination is definitely a great deal if you're on a budget. If you have more money you should take a look at the 1.4 lens which is even better but much more expensive ($350).