PowerResizer described here:
PowerResizer is a free program that
brings the window resizing/docking
function popularized by Windows 7 to
all Windows platforms. It is unique in
that once two windows are docked
PowerResizer will let you grab ahold
of any one of the edges in the
”border” are between the two Windows
and drag it to resize both windows
simultaneously, in case you wanted one
of them to take up a larger area than
the other. A really nifty feature.
Additionally, you can perform all
sorts of resizing behaviors using a
combination of resizing and hotkeys.
Another useful utility is AllSnap:
This program will make windows that
you might move around your desktop
’snap together’ (as, for example, they
do with WinAmp), or snap to desktop.
You can set the threshold in pixels in
the settings, and once your window is
within the range you define the
snapping-to-grid will take effect. It
can also prevent any Windows from
going off the screen. You can press
the Alt key (user definable) in order
to suspend the snapping action and
move windows normally.