What the best pasta shape to serve with bolognese?

Well, if you were actually in Bologna they would say pappardelle or tagiatelle. Which is not to talk trash on you rigatoni or penne fans, but that's the way it is.

If you get rigatoni or penne, make sure to get the rigate so that you have the ridges!

Thanks so much everyone!

tagliatelle or rigatoni

Rigatoni and penne are rigid enough to hold the sauce, and tagliatelle is wide enough to get a decent covering too. That's what I use when I'm in a Lady and the Tramp mood, rigatoni the rest of the time.
(Anna del Conte's book Pasta is a fantastic guide to pasta shapes / sauce matches)

My first instinct is spaghetti since that's what I'm used to.

Also, I just read this today which you may find useful: http://www.cooksillustrated.com/howto/detail.asp?docid=1133&Extcode=L1BN3AA00

I like rigatoni because the ridges catch the sauce.

spaghetti or linguine, hands down.