I really like Wikispaces. Not only have they been very supportive of many of the projects and events I've been involved with for several years now, but as an education vendor they interact with the education audience in a very authentic way. You will often see co-founders Adam Frey or James Byers hanging out in the "bloggers' cafe" at a conference rather than on the exhibit floor--and they do so in a helpful, non-self-promoting way.
Their "Free Wikis for Educators" program has given away some 980,000 free classroom wikis for K-12 education over the last five years (I've got to imagine that it will be a great moment for them to hit the 1 million mark). This program has done a really great job of helping Wikispaces to become well-known at the same time making a difference for in-the-classroom educators, a terrific combination of marketing to and serving an audience at the same time. Their ability to stay in this magic zone for education gives hope when other companies have started with the promise of free, then faltered and had to move to paid models--most of which haven't accommodated the individual educator well.
So it is really heartening to have heard from Wikispaces that next week they will be announcing that their program is being extended to higher education, at the same time announcing a new "goal:" to give away 2 million total free wikis for education. I'll let them pitch the value and savings numbers themselves when they formally announce announce the program. From where I sit, though, they've done something even more important than to save educators money: they have made a very real difference in the ability for educators and students to collaborate together, making the world a better place.
More information on their education programs is available here, including how to upgrade existing educational wikis to the free programs: