I don't know if your dad is into Pinball, but there's 2 great Pinball games on the Wii. Pinball Hall of Fame: The Williams Collection and Pinball Hall of Fame: The Gottlieb Collection. They're the epitome of 'good' casual titles that even gamers can enjoy. But again, only get them for him if he likes Pinball, as they're realistic Pinball Simulator games. Also, I'd say get The Williams Collection over Gottlieb if you can find it, but its out of print.
Other ideas are of course stuff like the Mario titles, LEGO Star Wars/Batman/Indiana Jones (if he happens to be a fan of any of those series), Metal Slug Anthology (if he likes Arcade shooters) oreven Mario Kart if he likes Racing.
I'd suggest Muramasa, but you said he's a pretty casual gamer.
Six upcoming games you should look into:
