Well, shift+u is hidden because it's broken. It'll take your money, but it don't do nothing yet.
But to answer the question:
1-6: switch to that number brothel. Works from most screens
D: dungeon
S: Slave Market
M: Brothel Management
M+Shift: Mayor's office
B: Bank
G: Girl Management
T: Staff Management
U: Upgrade Screen
U+Shift: Building Management (Broken)
A: Turn Summary
O: Town Screen
P: Shop Screen
And that's about it. Codes are defined in main.cpp, function handle_hotkeys(). If anyone can think of a shortcut that we don't have already, that's the place to add it.