In his new and already excellent blog, Léo gives us a great diagram that details the ASP.NET 2.0 page lifecycle.
Needless to say, this is a poster you can now find in nearly all offices here in the ASP.NET team at Microsoft. Thanks for the great work, Léo!
Read it, print it, use it every day!
UPDATE: updated the links to the new locations for these resources. The poster would probably need some updating in particular where callbacks are concerned but it's still very useful.