http://keepvid.com/
I always use this, it works from a java app.
It gives you a choice of download options and actually gives you a download link to the file straight from the youtube servers so you get it the exact quality as it was uploaded there, where as some other sites re-compress the files
e.g.
http://www.youtube.com/watch?v=ttuA1UEUAI0
Gives the download:
http://o-o.preferred.lhr14s07.v23.lscache5.c.youtube.com/videoplayback?sparams=id,expire,ip,ipbits,itag,alg orithm,burst,factor,oc:U0hPTldMUF9FSkNOOV9PRlRF&fe xp=914901,912602&algorithm=throttle-factor&itag=18&ip=0.0.0.0&burst=40&sver=3&signatur e=0D4D3AFA1CA996D02001DC9F7A2ED41CDA70969E.3D51D7E 3CC90C2FC18C2B320AABEF071BEFFFD62&expire=130971240 0&key=yt1&ipbits=0&factor=1.25&id=b6db80d54114008d &title=The%20Beautiful%20South%20-%20A%20Little%20Time%20[
www.keepvid.com]