Oh man, i think you'll love this one!
This is just a mockup, to see if ahk could support it. Apparently, it works pretty well.
Just press F8 and move the mouse. Press F8 again to stop unless you have gridmove or something else that allows you to move windows through keyboard installed, i don't recommend you try this software! [edit]
updated: move with ctrl+lbutton. Makes things way cooler
updated: added screen contraints: the virtual screen is now 9 times larger than the "real" screen. (think like this: middle one, and 8 around it). Can be customized to something else.
updated: added "keep active window on screen" feature. Works like this: when you alt+tab/select a window that isn't completelly on screen, it moves there. If you have just moved, it waits 5 seconds for you to focus another window and then it'll move the screen back to the focused window (which might be offscreen).
updated: fixed an error in "keep active window on screen"
updated: removed the "anoyingness" of the "keep active(etc)" feature
updated: added "jump one screen" feature
updated: removed "jump one screen" "feature", was driving me nuts. Added "multiplier" feature
updated: it doesn't ignore the taskbar placement anymore
updated: added the "move the screen but keep the window under the mouse in place" feature. just press windows key and drag with the right mouse button. This is a very useful feature for moving windows around.