Windows: Dual Display Mouse Manager is clever application that overcomes the problem of missed scroll bars and other GUI elements on multi-monitor setups by temporarily slowling down the mouse at screen edges. Check the animation inside to see it in action.
Dual Display Mouse Manager (DDMM) is a small portable application. You can unzip it and run it without any tweaking at all — we used the defaults with no issues, it automatically detected our monitor sizes. DDMM supports two mechanisms for helping your mouse cursor hit critical GUI elements. You can set it to a time delay (the default is 150ms) which makes the edges of your screen "sticky" for about a 10th of a second to give you time to grab the scroll bar or other element you were aiming for. If you want to get serious about keeping the cursor in line you can lock the cursor to the screen and enable temporary crossing to other monitors by holding down the CTRL key.
Check out the animation below to see how DDMM works. You may want to refresh this page to start the animation fresh for the full effect.
Dual Display Mouse Manager is freeware, Windows only. Have an application that makes life with dual monitors easier? Let's hear about it in the comments.