AdBlock is great, although it messes up the prettiness of some sites that have flash or applets that you want to keep in. But overall it's awesome.

Session Saver really helps. Love it.

I've also got DOM Inspector, OpenBook, QuickTabPrefToggle, Show Failed URL, and View in IE, as well as some extra search options like dictionary search, amazon search, etc.

1.0.4 didn't mess up any of the above extensions, but that is something to be aware of in new versions. Sometimes extensions will need to be updated as well.