Skribl is another online sharable whiteboard. I'm happy- because they recently added an embed widget for sharing and collaborating. The user interface is kind of home-grown, but it's functional. With a login, you can save your boards for later use. It's not the prettiest UI, but saving is key.
ReadWriteThink has activities designed from grades K-12. You can sort the activities based on what grade level you are looking for. It has activities such as word sorts, venn diagrams, poetry helpers, and many more literacy activities to be used whole class on an interactive whiteboard or individually.
EducationCity is a subscription website that features games for grades K-6 in math, language arts, and science. With the subscription, students can keep track of their progress in the games with the "success tracker", and then the teacher gets a compilation of student scores, broken down by subject and graphed to show how they are doing. It can be used individually with students, or in the "Interactive Whiteboard Mode" whole class/small group.
This is a page on the scholastic website that has interactive whiteboard activities for Earth Day. These activities include lessons on water conservation and recycling etc.
With a tool like Dabbleboard, you can send out the URL to a class so that they can interact from their seat, or get up and write on the board. Plus, with a saved link, you always have an easy artifact not attached to Activ or SMART software. Also embeds.
Reference: "Revolutionizing Instruction for Autistic Students Utilizing Interactive Whiteboards" was a presentation in ISTE's Technology in Practice Webinar Series, from September 2008. Information on this page could provide a starting place for further research/resources.
This site had online talking story books that could be used on an interactive whiteboard. This could be done as a whole class or used in small groups of students.
A compilation of SMART lessons from a school district in Wichita. The lesson plans are categorized for K-8th grade and address a wide range of subject areas. There are also lessons to be used with a Senteo. All lessons can be downloaded.
Scriblink is another tool similar to Dabbleboard, which can allow you to collaborate on the white board in real time, create graphic organizers, and save the URL. Check out a special message I made here.