There is also a 1998 study (in PDF format) of scientific research needs in this area.  The prose gets fairly bureaucratic after the first few pages, but there is a useful figure on page 37.

Congressional testimony on methane clathrate resources from the US Geological Survey.

Congressional testimony on methane clathrate resources from the US Department of Energy.

The connection between methane clathrate burps and rapid ecological change at 55 Ma was first made in a 1999 article in the journal Science.

The hypothesized connection between climate change and methane clathrates (sometimes called "methane hydrates") is now being made in other periods of Earth history.
Example 1.  (clathrates and climate change in the past 1 Myr)
Example 2.   (clathrates and climate change in the Jurassic)
Example 3.  (upclose and personal with clathrates on the continental shelf)

There is a central website on methane clathrate issues that is maintained by researchers:  www.hydrate.org.
It contains linked pages on the chemical structure of clathrates, the potential fossil-fuel reserves and possible links to past and future climate variations.