Join.me offers free screen sharing for up to 250 participants and it's absolutely free! It's perfect for businesses that are sharing presentations on conference calls or with clients or staff remotely. We've been using this at RedFlagDeals.com and so far it's been very reliable.

There is of course other other software out there for screen sharing, the most popular probably being WebEx, but what's nice about Join.me is that there's no registration required and it's dead simple to use. There's no catch, there is a pro version, but for most people the free version will work just fine. There's even a free iPad, iPhone, and Android app if you're trying to view presentations on the go.