How about Zooloretto? On the Underground? It's only slightly more complicated than TransEuropa I think. Maybe Nottingham. Quiddler? Detroit-Cleveland Grand Prix would work, though you'd probably have to modify the rules slightly.

Wow... on the underground is tough and can't really be played in 50 minutes, at least not in my experience. Can't Stop, Monza, FD Mini (might be too long?), Crokinole, Mastermind, and Fubi are all favorites of my 4th grader.

Tsuro is always an option - fast playing & hosts 8 players.

If you're trying to play games that are easily accessible, then my next two suggestions are "right out" - but I'm a big fan of Tante Tarantel and Igel Argern. TT plays w/3-5 players & IA plays with 2-6.

Nottingham might work but could be a little dry. How about ... Hey, That's My Fish! especially for 3rd graders. I'd also recommend Crazy Derby (Trendy retheme), Frank's Zoo, Cartagena and Mississippi Queen. Zendo or some other Icehouse games. You haven't used Through the Desert yet?!?

I just looked at the list you have from last year. Can you really play Bohnanza in 50 minutes? I've tried it twice, and didn't like it either time, primarily because it seemed to take forever to play, and there wasn't much game there. Maybe I misunderstood the game? I guess you could play fewer times through the deck or something - is that what you do?
I'm curious to see what games people recommend. I'm sorry I can't suggest any.
-Matt

Cartegena, Poison, 6 Nimitz or...dare I say it...24/7?

6 Nimmt, 24/7, Cartagena, Crokinole were all played last year and may resurface again this year. Tsuro is a nice option. So is Hey! That's my Fish! - there are a few others mentioned that I haven't tried yet so will explore.

Bohnanza: weren't able to play a full game, but we got through several hands and the kids really enjoyed it.

Some that have worked with me for that age group:

Cloud 9, Ka Ching (2 player only), Igloo Pop

It's an old post, but I've been out of commission for a while. Pickomino is a no-brainer for this age group, IMO. Niagra is also a nice fit (we play without the gem stealing, which makes it a snoozer for adults, but the kids still get a kick out of it). The selecta game Viva Topo might turn them off with the "kiddie" looks, but there is a fair amount of game there and teaches some great "gamer skills" (when to go for the score).

Whoops, when I said "Pickomino", I meant "Pick Picnic." BOth are winners, but Pick Picnic is always a hit for me.