Downloading Youtube HD Videos

What is the best way to download the HD version of videos on youtube? I've tried a couple methods (firefox download helper and bookmarklet), but the quality isn't as good as it was on the site.

Just a quick question, is downloading youtube videos allowed?

i don't think it's not allowed...they don't own the rights to the material uploaded, right? not sure if they can not allow people to download material that they don't have rights to, but i'm not 100% sure.