(Undocumented feature of FSX).
A descriptive label can be displayed around 1500ft above airports in FSX. It cannot be configured through the standard key controls menu, so you have to modify a file by hand: standard.xml, located in c:\Documents and Settings\<user>\application data\microsoft\fsx\controls (under XP, vista should be different)
Add an <Entry> block in the first simcontrols.map (at the beggining of the file):
<Entry> <Key>SHIFT+U</Key> <Down>TOGGLE_AIRPORT_NAME_DISPLAY</Down> </Entry>
SHIFT+U will be the key shortcut used to toggle label display.