Anyone know a free and reasonable quality way to sample from youtube or from online audio in general?
Try http://www.listentoyoutube.com/ ?
Or, just watch the video in HD and record it realtime into any audio app.
Video Download Helper is a fine Firefox-Extension which allows you to download Youtube-Video in mp4. With the program “Super” or Xmedia Recode you can convert the video to any desired format such as ogg or Mp3 or wav.
There are so many ways I don’t even know where to begin! 
I used a ‘new’ way (for me) two weeks ago that worked exelent.
Use a free video downloader to download the video with the sample you like.
Now, I use Gomplayer as my default videoplayer and that has a very handy audio seperation function, just scroll to the part you want and press record, press stop when you want it to stop and there you have your perfect .wav sample!
The .mp3 downloader bytesmasher suggested doesn’t seem to work with normal videos, only with songs that actually have an .mp3 file uploaded with em. I have been fooling around with that thing for half an hour weeks ago.
I use a program called SOUNDFLOWER <i think it’s for MAC though>
Once it’s installed, you set the main output of your computer through it, and then your renoise/(other app) input through it.
Voila
You can’t upload mp3s along with youtube videos
Even more easy:
You take this video:
And instead of youtube.com/watch?v=gOYRfuhxMmQ you write: 3outube.com/watch?v=gOYRfuhxMmQ
Oh, and the song is by me 
Neither of the formats displayed there are sound formats Marc … you’d have to convert.
Well, I have aac support in audacity. Installed the plugin and can load the mp4 directly… Okay, converting with audacity is converting, though. You’re right.