As a SizeUp equivalent, I've been using WinSplit Revolution for years, and it's an amazing keyboard-based window manager that is especially useful for large / multiple monitors. It's fast, has a small footprint, and is completely unobtrusive once you've configured it to your taste. I use it in a development environment where I have an IDE, graphics software, text editor, wiki and multiple browser windows all in use at the same time. I couldn't work without it.