I'm a newbie to the sport but I've seen highlights of Jonah and a few full games of him I got on dvdr from a friend. Truly amazing player, he's one of the first players I saw when looking into the game, total shame about the health problems. Fully deserving of all the praise he gets and then some.
The Legends DVD thing posted earlier is quality. There used to be lots and I do mean lots good highlight videos on youtube a couple years ago but majority got deleted.
I think I'm lucky to have stumbled upon this one documentary thing about Lomu coz it's not easy to run across it amidst all the 20 second long Jonah Lomu vids. It's seven parts and it's got a couple short bonuses to it also, one of them is a highlights flick, so if you just wanna see some of Lomu's great tries check this one outt (don't forget to click "watch in high quality" wherever possible)