I think the All-Kurt Russel Lead is great, myself! That's all we need!
Seriously though, I'd discount most superhero characters, and big name mystic types. Angel would probably take over the whole operation, Buffy definately carries as much weight as he does--we need that kind of balance.
For a modern day league, though, I did have a few more ideas
L from Death Note would, I think, be a perfect fit. Investigative genius, weird and antisocial enough that he's got a great dynamic with a group, and he'd be excellent for a mission control area.
I second the idea of Harry Dresden over Harry Potter, though I've read neither of the books. In the same sense of needing some supernatural weight, what about one of the Ghostbusters? They're probably out if we push for just literature (I'll give L a pass, comics count...enough).
The whole "twenty minutes into the future" thing of Snow Crash might disqualify him from a 'modern' league, but Hiro Protagonist would make a good tech support, and it never hurts to have a badass swordsman on any team!
I like the idea of having a Highlander on there, along with Scully. Or at least somebody from the X-Files! But again, literature, hmm...I'm trying to think of other books that have made a splash in the last twenty years...um...maybe Tyler from Fight Club? I"m not sure how that would really benefit the League, though...
If we discount the literature only rule, we could probably throw in most of the leads of CSI, Grissom especially. Though again, with L, probably don't need anyone else on that level. Team needs an adventurer, that's what it needs!