Well, I don't know any well known games made using uGUI but u can check some of the games which i helped develop and they are using uGUI.
Jump and Rush
Poptropica
I also switched from NGUI to uGUI back when Unity 4.6 was released. At the time i felt NGUI was still better and uGUI just lacked many of the features that NGUI had. Now i feel uGUI is better. Still some tools i extracted from NGUI which uGUI lacked and edited it to support unity UI. Those were tween library and some editor tools. Of course we have iTween, leantween, etc. but interface which NGUI provided through inspector was better.
I suggest you to switch to uGUI. Everything possible with NGUI is possible with uGUI also and it is much more efficient performance wise also. It is open source
like NGUI .
Check this link for source : bitbucket.org/Unity-Technologies/ui