Here are a few of my favourite young actors I think are worthy of keeping an eye on.
Ben Foster - http://www.imdb.com/name/nm0004936/
I first saw this guy in Alpha Dog, which I really liked, also he was quite good in 3:10 To Yuma.
Clifton Collins Jr - http://www.imdb.com/name/nm0004286/
I really like this guy. First became aware of him years ago in a movie called The Stoned Age. Never thought he'd do much back then but imagine my surprise when he started showing up in movies more recently, namely; Extract, Crank:High Voltage, Boondock Saints 2:All Saints Day, Star Trek and I marked out a little bit when I saw Scott Pilgrim vs The World and he had a small role. If you don't know him - you will.
Joseph Gordon Levitt - http://www.imdb.com/name/nm0330687/
Who would have thought the kid from 3rd Rock From The Sun would end up as, in my opinion, one of the very best actors going at the moment? He is the ONLY actor I could imagine that could reprise Heath Ledger's Joker - not that I would want that - but this guy is the shit. I saw him in Killshot and all I could think of was how good he was. Also great in 500 Days Of Summer - this is a good movie disguised as a chick flick. Worth a watch. He's also in G.I. Joe and 10 Things I Hate About You.