As mentioned in Robert Scoble's "Office in a Cloud" article, here is a tremendous database of useful online applications put together by Ismael Ghalimi, creatior fo the Office 2.0 Conference:
http://o20db.com/db/setup
You're bound to find something useful and/or fun in here. Have you seen Gliffy yet? It's like an online version of Visio. How about the custom forms available at Wufoo? These are not entertainment sites (although I admit to smiling while using them). They are full-blown applications for creating (and, more importantly, sharing) drawings and custom forms.
Click here for my sample Gliffy diagram. Thanks again to Fast Company editors for providing useful information for hard-working small business owners.