Zero-K's UI (free and open source rts game based on the Spring RTS game engine) gets pretty much everything right. Most players who come from playing it who play other RTS games refer to themselves as being 'spoiled' from how good it is. The UI layout itself looks pretty standard but all the magic is in how easy it is to do tasks without enormous amounts of clicks. It's so easy that it's possible to play the game effectively only clicking about 12 times every minute. Buildings can be built in lines or grids with custom spacing by holding modifier keys and dragging out your mouse, every command can be queued using shift and inserted into an existing queue using other modifiers, units can be put into formations simply by right click dragging a line formation out, paths for individual units can be made by dragging a line, holding modifiers can allow you to do this for groups too, and the repeat button allows for a lot of automation, both for factories and allowing units to do things like go on a specific patrol path or rebuild destroyed buildings.
It also has a few extra interesting systems like selection priority where you can press a little numbers in the command panel to set the priority of a unit to be selected, holding ctrl while using a guard command (and other combos of modifier keys) allows you to make units guard another unit in a
circle formation, circle around them instead of standing still, or stand relative to the units' facing. Similar to PA, if you zoom out enough units will turn into icons instead (unlike AIWII's current system which is to always have the icons above units, creating painful clutter). In general the game is great in both handling UI for managing huge amounts of units and small squads.
You can see a few basics of the UI of ZK
here and
here. The layout of ZK's ui is changing a bit often as it makes is sprint towards its official Steam release and some screenshots on the wiki are a bit old (game's always been available for free and the Steam release is for publicity so you can still check out the game's UI yourself regardless).
Last cool thing about it is that since it runs in the Spring engine, the UI is completely customizable. Panels can be moved around and resized as you please and the UI can be extended (and even automated) through lua scripts that the game calls "widgets" which run entirely client-side (this can mean advantages over others, I suppose. Doesn't allow cheaty things of course and the unit AI is made in such a way that micro isn't required).
