subtle is a grid-based manual tiling window manager with a strong focus on easy but customizable look and feel. In comparison to other tiling window managers, subtle has no automatic tiling of the screen size in any way. Instead, windows are arranged according to positions inside of a grid. These positions are called gravities.
wumwum is a window manager manager. The idea behind wumwum is to turn any EWMH-compliant window manager into a tiling manager a la "ion" or "awesome". wumwum works by using wmctrl, and adapts itself dynamically to the active window manager. All functionality from the underlying window manager is kept when under wumwum, making it ideal for beginners.
i3 is a dynamic tiling window manager. Its key features are correct implementation of Xinerama (workspaces are assigned to virtual screens, and it does the right thing when attaching new monitors) and XrandR support (which is still unfinished). Both horizontal and vertical columns can be used in tiling. There is a special focus is on writing clean, readable, and well documented code. i3 uses xcb for asynchronous communication with X11, and has several measures to be very fast. i3 is primarily targeted at advanced users and developers.
x9wm is a clone or fork of the 9wm and w9wm X window managers. It is a light alternative for the Mac OS X desktop. All of its source code is contained in a single file. It supports an alterate red colored cursor. It is very light on resources, quite fast, very simple, and easy for long programming, editing, or Web work sessions. You can blend it with Nitrogen and Wbar to create a simple but elegant interface without iconic or stylistic clutter. It does not decorate windows with borders, and it is modal, controlled with the mouse.
Lunchbox is a dynamic tiling window manager for X11. It allows windows to be resized by squishing them against the edge of the screen. In a step away from the desktop metaphor, all programs are given a separate workspace and unique arrangement of windows, and any window can become the desktop. It offers an in-built scalable tab replacement called the Title Menu, which allows any window to be swapped with any other window that fits, allowing very fine grained control over the layout of the screen. Finally, although many windows default to tiling, any window can be changed to a Floating mode, which dialog boxes default to.