Need some recommendations for online collaboration tools

One of the toughest things for me to overcome as a distance learner has been how to collaborate with my students and other instructors. What sort of tools have you all used to work together in group projects or other collaborative learning settings? I try to work in at least one group project per semester because I think it is important to be able to work effectively with other individuals on projects in remote locations once in the workplace. My students always seem sto struggle with these projects and communication with others is always the biggest issue.

I've used Google documents and their associated tools in the past but wasn't hugely impressed, but recently have been trying out Proofme (link removed by Moderator) and have been pretty impressed. The free accounts have 5gb of storage space with no limits on the number people who can edit and access documents. It integrates pretty well with other online storage websites like Dropbox and Onedrive and has sharing capabilities with almost all social media outlets. I think it would be really good for marketing courses where you need multiple people working on a product design all at the same time and giving feedback on others' work.

With that in mind, what are some of your favorite ways to stay hooked in and engaged with other students and instuctors? Thanks!