Microsoft Office includes some great programs, but it's often really hard to do simple things (for example, MS Word styles). In this respect, Powerpoint is probably one of the worst culprits. Putting aside aesthetic complaints, a casual user can find it pretty tough to create some simple slides or graphics.
Gliffy is a solution to Powerpoint woes. Another AJAX, web-based program with the feel of desktop software, Gliffy contains a simple drag-and-drop interface. The site contains lot of shapes and frequently needed images for designing an apartment floorplan or a computer network. It's very easy to alter sizes, shapes, and colors. Afterwards, you can even publish the image on another site (sounds perfect for Craigslist). Here's our apartment: