For white phosphorous, I think there was a controversy regarding alledged use in built-up areas by the US military in Fallujah during the re-seizure of the city from insurgents in 2004. Similarly, Israel alledgedly used WP during their invasion of Gaza last year (I think it was). The problem here is that it is sometimes used as illuminator over a battlefield, which I think is allowed. The problem is when it explodes right above some civilians, and consequently fries them (sorry for being callous)
Regarding cluster munitions, yes the recent agreement would be a huge step on the way on banning the use, and seeing how many countries signed it, it would be able to assert itself as customary law, even if the major powers refuse to sign it (but seeing as how these are major powers, they probably would still use them in the event of a real war). In the past decade, I think only Israel, Russia and Georgia have been accused of using cluster munitions, at least in built-up areas. Did the US use any in Iraq?