What kind of product you have? There are several start-up video types, depending on the type of the product. Making real life videos (humans in video) is always easy but to be explanatory you have to make extra addition, with 3d or 2d video video editing softwares, if it's software or hard-to-understand SaaS etc. If you don't want to bother with these editing softwares like adobe after effects, final cut pro, 3ds max etc., making cartoon videos are always a good idea. Just look at dropbox's first video, how simple it is.
1. http://startup-videos.com/
2. http://www.quora.com/What-are-some-good-examples-of-startup-...
3. http://www.demoduck.com/samples/