I would also suggest to use PowerPoint (or something similar, e.g. OpenOffice Impress) and to keep your slides as clean and simple as possible. An advice I got from a professional trainer for scientific presentations was to avoid slide transitions, fancy effects like image reflections, and (unnecessary) animations. However, if you present 3D visualizations, I think it is always very impressive if you embed interactive 3D models in your slides that you can rotate and zoom instead of a simple screenshot (you will need a specific applet for this like http://www.3ds.com/products-services/3dvia/3d-xml/player/).
There's one new great tool that I'm using recently to build my research figures and presentations, it's very easy to use and it has a gorgeous cientific illustrations database, you should give it a try: