Two types of evaluation that seem appropriate to collaborative learning situations are "authentic evaluation" (since collaborative learning experiences are typically "real-world" ones) and peer evaluation (for obvious reasons). See also the section on rubrics and authentic assessment in this chapter.
Peer assessment and peer review
Pitch is a journal about e-learning that uses an open peer review mechanism involving all readers rather than just a couple of designated reviewers.
More material on peer assessment and peer review to follow later.
Diagnostic assessment for collaborative learning
Profiler is an interesting tool which allows individuals to identify their points of strenth and weakness in a learning domain and to see who else in the group can be consulted for help with areas in which they are weak.
An interesting reversal to the usual evaluation relationship is where students evaluate lecturers, e.g. at sites such as RateMyProfessors.