In no order:
Cash for Clunkers
half crank engines (IMO)
Surprised nobody mentioned non-adjustable carburetors yet. I love my PB-250 Echo except for that I basically have to warm it up for 5 minutes.
For all the Briggs haters, I really don't get where you're coming from (please do tell me your experiences). I love my 675 and 725EX quantums on my Snapper 21'' mowers. I've never had a Briggs engine on a riding mower so maybe that's where they suck, but my briggs 675 is like 6(?) years old and has had one oil change and no other maintenance (I know, I know) but starts one pull and is powerful and reliable. More reliable than the GXV160 on our commercial grade Snapper 21''.
Maybe I'll think of some others later, I'm sure I have more.