I also rank RockNRolla highly. It's not as good as Lock Stock or Snatch, but it's the best thing Ritchie's made in a long while. It's refreshing to see him getting back to his roots.
I also enjoyed Slumdog Millionaire. Just about all of Boyle's film have been of a high caliber (not The Beach, which he can't really be blamed for given how much the studio fucked him over). However, while Slumdog was excellent, I don't think it was his best work. Because of this, I'm a little disappointed that he's just now getting the recognition, meaning golden globe/oscar/Palme d'Or, he deserves (at least among those who aren't die hard fans of his). I rank Sunshine, 28 Days, and Trainspotting above Slumdog. Though, Slumdog was certainly more uplifting and mature than Millions and Boyle was able to perfectly capture one of the most attractive aspects of Hindu/Indian philosophy.