I recommend you a free tool that can help you download youtube video easily. and it can convert the donwloaded video to many portable player or mobile phone. such as, iPod, iPhone, Nokia, BlackBerry and son so.
you can get this tool at here:
this free tool called "Next Video Converter"; Beside downloading YouTube video, Next Video converter can also help you convert video and Rip DVD to most popular video formats including DVIX, Xv iD, MOVE, RM, RM VB, MPEG, VB, DVD, MV, and AVI to MPEG-4 movie format for iPod, PSP, PS3, iPhone, XBox360, Zune, Apple TV, Archos, iRiver PMP, Epson Player, Creative Zen, Rubi Blue, Sony Walkman, Commodore PMX, Palm TX, Game Boy, SmartDisk, Windows Mobile Smart phone, Nokia, BlackBerry, Ketti, LG, Sony-Ericssonon, Samsung mobile phone, etc.