I think the Java runtime installer asks to install a toolbar. There is something else that I can't recall (flash runtime?) that asks to install the Ask.com toolbar all the time as well. Some popular open source projects too (PDFCreator).
The flash download page asks you if you want to install an antivirus, I believe it's mcafee.
It's funny, though, that I encountered a "not so bright" person who simply told me "oh, I didn't know you could opt out, I was always uninstalling it afterwards".
You can also block the ask toolbar from downloading by killing toolbar.ask.com or the entire ask.com domain. It most certainly will not be missed.
