Six-String Samurai isn't great, but it's so silly and fun that it's certainly worth a recommendation.
Hmm, well there's this trio of films I've been meaning to rewatch one of these days: License to Kill, Flash Gordon and Lion in Winter.
Apart from Lion, they're not "serious" masterpieces but they're all good. The reason I want to watch them in a near-marathon is because all three have Timothy Dalton acting. Good enough for me. Or maybe I should just rewatch Lion, it's a great film. King Henry invites family over for Christmas. Hilarity ensues. Great acting abound.
A while back I discussed some films with a friend. Portrayals of childhood trauma in particular. Pan's Labyrinth and Tideland came up and are good, of course. I think Pan has more critical acclaim, but Tideland is my favourite of the pair (I'm a Terry Gilliam fanboy so that doesn't really count I guess). Plus Tideland has Jeff Bridges and a guy who kind of looks like young Ron Perlman.
Seriously speaking, Tideland has some pretty grim stuff, I'm oddly excited about rewatching it once I get some broodlings of my own. I should probably add that the grimness is strictly in the mind of the viewer. Visually it's very ages 7-13 and up (disclaimer: dirty euroliberal here).
If you liked Oldboy, I'd suggest Sympathy for Lady Vengeance. It's part of the trilogy (only thematically linked, no plot relevance between them) and in my opinion best of the trio. It's about a mother who gets falsely accused and thrown in jail. Then she gets out. Very good, very emotional. Possibly silly for a few moments (in a bloody Korean revenge film silly way).