A lot of newer videos now have gotten a simple link that you can click to view a video on Youtube in high quality. However many older videos are still without it, and there's a very simple copy and paste way that you can get higher quality videos, should they not have any option to actually view them via the link under the video.
&fmt=18
Just copy this, and paste it at the very end of any youtube video. If it has high quality already, it will just turn it on, however should it not have it, on many videos you will find the quality has greatly improved.
Here's a simple link, basicly a very simple 'test' you can do this with, as well as an example.
EDIT: The second link will not work in better quality streaming as it's being linked. To actually see the second example, simply click the 'Youtube' link in the green area above where that video would be shown, and it will simply bring you to physical youtube video.
Original Link: watch?v=4OQdTNwnpws
[ame]http://www.youtube.com/watch?v=4OQdTNwnpws[/ame]
(notice how it has no option to go into high quality mode on the site)
Higher Quality: watch?v=4OQdTNwnpws&fmt=18
[ame]http://www.youtube.com/watch?v=4OQdTNwnpws&fmt=18[/ame]
For those too lazy to even click on links, here's some screenshots as well.
Please note however, this does not work with 100% of all videos. Some videos were probably well... naturally crappy on uploading.