Stephen Marsh's blog is a growing resource of creative and fun ideas and technologies relating to collaborative work - e.g. on trust and reputation in distributed environments, affective computing and much more.
Resources about e-learning (often but not necessarily collaborative)
Online Learning Daily, edited by Stephen Downes, often contains material on collaborative learning and learning objects. In addition his very frequently updated edu-RSS lists new postings on other sites related to e-learning.
The e-Learning Centre is a long running UK portal founded in 1994 by Jane Night with stacks of articles, software reviews and events.
Brian Lamb is the "Learning Object Discoordinator" at the University of British Columbia and maintains a weblog called Object Learning on "reusable media, weblogs, and lots of fuzzy stuff nearby..."
The Encyclopedia of Educational Technology (EET) is "a collection of short multimedia articles on a variety of topics related to the fields of instructional design and education and training." There is unfortunately no over-arching structure (articles are alphabetically organised) and articles varies vary in quality, but no doubt there are some gems to be found.
cetis (centre for educational technology interoperability standards) "represents UK higher-education and further-education institutions on international learning technology standards initiatives" - sounds boring, but actually contains many useful resources. Also, it provides some good introductions to the issue of standards in e-learning.
Ray Schroeder's Online Learning Update contains daily links to and short descriptions of online learning related items.