I agree with Craig that The Craft of Research is a great book for all disciplines. Although it is about writing primarily, it has a very good section on communicating evidence visually. And, as Craig said, all that is true about good writing also goes for good presentations. Any presentation or writing that is worthwhile listening to or reading will require some research.

I'm in literary studies, so my challenge is coming up with visuals that make sense in the first place. I don't have data to show, just text, so I sometimes use mind-map- like visuals, or images that relate to the text (e.g. the frontispiece image of the first edition, or the cover of the book I am talking about), or even graphs that visualize textual structures (e.g. character relations). It is very difficult in any discipline to come up with visuals that are memorable without being tacky (e.g. it would not go down well in most humanities audiences to use cartoon-like image metaphors as I have seen them used in other disciplines).

I always like presentations best that use the least amount of text on the slides and use the screen to clarify their point visually rather than trying to cover the whole presentation in endless tired bullet-points.

I don't think even a hostile audience will dismiss you if your argument is sound -- adding serious looking evidence to your presentation will not make it more compelling.