Is there a keyboard shortcut to cycle between windows in the current space?
Solution 1:
Move focus to active or next window (⌃F4). It cycles through visible windows (not applications) on the current space.
I've assigned it to ⌥⇥ myself, and assigned ⌥T to what ⌥⇥ would do normally: d=~/Library/KeyBindings; mkdir -p $d; echo $'{\n\t"~t" = insertTabIgnoringFieldEditor:;\n}' > $d/DefaultKeyBinding.dict.
Solution 2:
I don't know of any keyboard shortcuts; but consider the following program.
http://manytricks.com/witch/