You can make an online “bulletin-board” with virtual “post-its” (called “popplets), just like in Wallwisher. And, except for the fact you have to register to use it, Popplet is just as easy and, in some ways, easier to use with a lot more functionality. With Popplet, you search for images and videos on the Web directly within the “popplet” instead of copying and pasting the url address (as you need to do in Wallwisher). You can draw within the “popplet” and it doesn’t appear to have an limit on the number of characters you can use. You can connect the “popplets.” You can also embed the whole thing.
Having to register for it does offer a minor drawback. And you have to be registered in order to participate in collaborating creating the series of popplets. However, for me, at least, I see that as an advantage, since I generally want my students to create something that cannot be changed by others (you can read how I use these kinds of apps for categorization activities in The Best Social Bookmarking Applications For English Language Learners & Other Students, where I’ll be adding Popplet).
The other negative, of course, is that you still require an invitation to join Popplet — I receive mine, though, less than twenty-four hours after I requested it. Try it out and let me know what you think.