Now on topic, one thing I wish is UI improvements:
Better filtering of objects on the tracking station, such as showing only objects orbiting or landed at a chosen parent, showing only objects with a pending maneuver node and such;
Filtering of missions during gameplay, allowing to filter out missions that are unattainable with the current craft;
Sorting mission options at the mission control, such as by reward value and deadline;
A listing of stored experiments instead of having to click 'keep experiment' dozens of times when checking stored experiments;
Ability to take only specific experiments;
Telling what speed and altitude an object will be at a given point in it's orbit;
edit: Another thing
Finding an object by searching it's name, it's a pain in the ass trying to target a particular asteroid for capture when there are dozens of them