For the last year, I've been struggling to find a wireframe tool that was simple, added collaborative tools, and actually had interactive components that mimicked how HTML objects and elements actually worked. My search just ended with Hotgloo.
From their site: HotGloo is a rich internet application designed to build functional online wireframes for a website or web projects. Create and share fully interactive online prototypes. Collaborate with colleagues and share the output with clients. HotGloo is the perfect match for anyone working on web projects.
What I like best about Hotgloo is the ability to add functioning elements such as tabbed interfaces, accordions, maps and charts. Every element you drop on the page is actually interactive… so you can provide your client with a working, interactive wireframe rather than simply still pictures that provide no interactivity. This last week, I had to send wireframes to an agency and, with Hotgloo, it took me less than 2 hours to layout an entire site with multiple pages and interactions.
Your client even has the opportunity to drag notes onto the prototype and comment or leave questions throughout. If I had one wish for Hotgloo, it would be to ask for sub-pages. Currently, all the pages reside in one list on the sidebar. Having categories or the ability to add a page under a page would be great to organize complex sites or projects.
Pricing is extremely affordable, ranging from a single user at $7 per month to an Enterprise version with unlimited users for $48 per month. If you're a student, you can pay $5 a month for the team license!