Here are some of the styles I recommend for your documents/ presentations/ e-learning modules. Some I admit are more retro than the others and may not appeal to your taste, but oh well!
All in all, I find Microsoft illustrations quite flexible when it comes to their use in documents and presentations, particularly because I'm not limited by the original composition and context of the images and that I can actually choose to combine element from different images to create the custom scenes that I want. Again, its important that these images are used in a consistent fashion so that your audience gets a uniform look and feel that doesn't ever look like a forced collage!
Read more about this in Tom Kulhmann's post here.