Norton, McAfee, in fact most virus scanners.

Plenty of examples I've heard about but haven't actually used myself so I can't confidently assert the quality of the software. But Windows ME, Norton, and McAfee, I have personal experience with.

Oh, and also Windows Vista.

Plenty of badly-written open source software, too; won't argue against that. But one of the biggest reasons, for me at least, why I prefer to use open-source software rather than commercial if I have a choice is bug fixes. I've reported over a dozen bugs against open-source software I use over the years; most of them have been fixed (in a couple cases I was able to fix it myself). I've rarely even been able to report a bug against closed-source software, let alone get those bugs fixed. So even if if were true that commercial software as a whole has similar or better quality than open-source, my personal experience is the other way around: open-source quality gets better over time while the closed-source software that I have to use (lacking open-source alternatives) doesn't improve the same way.

Windows ME, Windows Vista, Internet Explorer, Adobe PDF Reader, Siemens Step7, Norton, McAffe, the list goes on. If you look at it as a function of terribleness * users then corporate ware takes the cake. There are loads of terrible open projects but nobody uses them.