Every sorority goes through open house during formal rush. So this should help.
Open House has a couple of goals. Keep people interested in rushing. Make all the rushees want your house.
If every house does slideshow, speech, coversation; try mixing it up some. Have the brothers and rushees chat, then speech, then presentation. Just doing it in a different order could make you stand out.
Also, I really hope you don't mean an ACTUAL slideshow.
If you are, try powerpoint or videos on screens around the room.
Try to pick some cool up beat music to go along w/ the presentation. Also, a little light show never hurts. Be it lasers, disco ball, or glow sticks. Rushees remember the house w/ the cool lighting.
If in doubt, ask some of the sororities on campus what they do during formal rush. What works on girls should work on the boys too.