Recs.
Updated
i3 is a dynamic window manager that is targeted at advanced users and developers. It uses clean and documented code in order to allow for ease of configuration.
SpecsUpdate
Pros
Pro Fully configurable (including tiling)
One of the biggest attractions of i3 is that it can be configured just about any way the user likes. Ranging from custom keyboard shortcuts to placement of opened apps, it is up to the user as to how they would like their window manager to behave.
Pro Excellent documentation
Every feature is thoroughly documented (including examples), and documentation is kept up-to-date. For questions that are not answered by the i3 user guide, because they concern tools outside of i3 for example, there is the community question & answer site.
Cons
Con Missing "include" possibility in config
While pretty good and easy to use for common tasks, the configuration language is missing the include directive common in other languages. You can use a workaround - a shell script to config parts on demand. It would be best if this were built-in however.