Dropbox
If every student in your class has dropbox it would be a very handy tool because of the simple fact that you can ensure each student has all the same information (rubrics, assignments, announcements, etc.) in one spot. The best part is you won't have to keep making photocopies of things you know you already handed out twice because everything can just be on the web! I think using dropbox in this way would be suitable for any grade as long as you showed and modelled for the students exactly how to use it and access files, etc. For the older grades you could also have them submit assignments via dropbox. Even better you could have students share assignments on dropbox for peer review prior to submission! This way you are incorporating some assessment as learning.Jennifer Carey offers some great advice as to how to use dropbox as well as a step-by-step explanation of how to get your students started on it!
Google Drive
Google drive really makes it possible for you to have a paperless classroom! Google drive is great for collaborating with parents and sending home announcements, permission slips, etc as most people already have a google account or something similar. By doing this, teachers are in close contact with parents and can always be assured they are receiving important documents. Similar to dropbox Google Drive can be used between students to share assignments. It is extremely handy because all members of a group ca be working on the assignment, editing it, etc and they do not have to be sitting across from each other at school I would probably be more apt to use a tool such as Google Drive with older students as they may be doing more group work which would require them to meet outside of class time.
Google Hangout
Google Hangout is a great tool to get your students familiar with, especially in older classrooms (grade 6 up). This is a space that allows students to drop in and out, check in, ask questions, bounce ideas off one another, etc. If students need clarification on an aspect of homework or something they can check the hangout and ask their question to anyone who may be on. Furthermore, teachers can schedule tutorial time on the hangout and help those students who may need extra explanations, etc. The only problem with this is that teachers do need their free time as well - we cannot be available 24hrs a day. As discussed in my Ethics of Teaching 4381 course, teachers must be careful as to the amount of time they are spending interacting with students outside of class time (even though it is purely for teaching purposes). We cannot be available for our students all the time, nor is it appropriate to do so.
Crowd Sourcing
Crowd sourcing is a teacher's dream! Beg, borrow, steal - this is what I have been taught to do as a new up and coming teacher. Crowd sourcing is especially great because the people are not concerned with money (meaning it is typically free). Some great teacher sites for this are smart exchange, better lesson, and teachers pay teachers (although not every thing is free on this site).
As for students - If you could set up a private crowd sourcing type site that only the class could access then students could post their notes, projects, etc as a way to work together and share their ideas. This would probably only work well in older grades, however, this could also raise an issue or 'copying/cheating' where students feel like they don't have to take notes for themselves because they know someone else would post them.
Significant comments -
http://danuedportfolio.weebly.com/2/post/2013/07/collaboration-cloud-computing.html#comments
http://joansjournal.weebly.com/1/post/2013/07/topic-7-collaboration-cloud-computing.html#comments