After MadOgre’s post about the new Barrett 25mm rifle (the XM-109) I did a quick search and here are some of the links that I came up with. First off, the always excellent Murdoc Online has a page dedicated to the X-Weapons- his is one of the best sources online about the XM8 too. Worth a look.
Strategy Page also has a nice image of the XM-109 and a brief discussion of it here, though the image is the same as the one on Barrett’s own page here. Small Arms Review also have a PDF about the “Payload Rifle” here.
Another new weapon to look out for is the XM307, the replacement for the .50 cal machine-gun- it can be quickly switched from .50 cal to 25mm. All in all a fairly exciting time for new military weapons.