In case you haven't noticed, Android apps and overall Android software are generally lacking in the UI department. Apps are normally based on functionality and not looks so leave us with a bad interface and features we cannot find for the cluttered UI in front of them. What we need is a way to customise Android, and a place to find tweaks and customisations.
One such place is the Android UI Design forums. Here, you can find a number of very interesting topics regarding the MIUI ROM - in my opinion, the most beautiful ROM for Android. There are icon packs in the forums, for example the Signa packs, themes, tutorials and many more useful things for any budding customisers.
If you are looking for good apps and UI concepts rather than ways to customise your phone, check out UltraUI, part of the UltraLinx Network. UltraUI is full of great UI designs and amazing inspiration for Android, iOS and other OSes.