No Thank You Evil is great for younger kids, but I suspect that a 10-year-old who enjoys Dominion could jump straight into "real" role-playing games if he is inclined that way. My eldest started playing D&D at 11, I think, and routinely plays with adults and with other teens now.
I remembered a couple more that are big hits in our house - Ricochet Robots and Micro Robots. We have had quite a few big family showdowns with these, including multiple 4-way ties in Ricochet Robots (possible when the last chip drawn can't be played because it has too easy a solution). Ricochet Robots, in particular, has a nice "leveling" mechanism that keeps it from being too much of a runaway victory when people are reasonably close in skill, but not equal.
