Can you describe a required online science course that used discussion well? I am re-designing an introductory biology course for an online summer session - five weeks of hard work for the students. They are mostly lower-division students who are re-taking the class or are adding bio as a minor. 

I can transmit content no problem with videos and outlines. What I'm hoping to do is also present students with problems to solve and encourage them to work together through these difficult, new presentations of the material and help each other. I'm using Moodle, so this will likely happen in the discussion fora -- though I'm open to using a third-party tool.

Generally, students are not motivated by the joy of discovery, particularly in a double-time online environment. But they are willing to do work if it is clearly related to how well they will do on exams. I'm looking for data - has anyone taken (or taught) an online SCIENCE class that had group and application work they felt really improved their understanding of the material? If so, please describe.
The best experiences I have had in working in group, in terms of exogenous motivation, were encouraging competition: define a problem, divide your students into groups, set a time limit and give a reward to the first/best/any-criteria-you-consider group. 

Live discussions/meetings can be more helpful that a forum in this sense: the probabilities of engaging in a fruitful dialog increase. 

You may also want to take a look to gamification techniques: 


http://en.wikipedia.org/wiki/Gamification
http://en.wikipedia.org/wiki/Gamification_of_learning


If students are not motivated by themselves, the internal pulse of "trying to win" at something may do it, gaining knowledge along the way, without having the feeling of "doing homework".