You need better images - or more images than are available in the clipart that comes with Office (good plan - using the same pictures everyone else uses is such a bore!)
The Solution
I bet you already know it - even if you don't really know it... the best place I've found is Google

Once you're there, click on Images, and enter your search terms the way you would do do any other sort of search.
Once you find an image (or more likely, images) you can save them right from that one page - its often better to click on the picture itself and then click on See full-size image first. Then, when you save it, it will often be more versatile.
Another link that can be very helpful is Microsoft's clip art collection. There, you search for images, tick the boxes below any that you want, and then look for the 'Download clips' link on the left. Clips will be downloaded right into your clip art organizer, where they can be organized the way you want.
