I already posted this in another area, but, passing out bananas and having classmates put condoms on them (many ppl don't know how to do it correctly) is a fun way to end the presentation. Bananas are cheap and sometimes you can get free condoms from the student health services. If not I think they sell them in packs of like 48 for cheaper. I actually did this w/ a group of seniors for a community intervention and they loved it! I wish I had it on videotape!
To address the comment about putting the condom on your foot to prove it would fit... My friend was dating someone (real jerk, btw) who kept saying that he was "too big for a condom". I took a regular sized one (not a Magnum) and rolled it all the way up to my elbow. Then said "OMG, your bigger than this?"
For work/study I taught a required class (incoming freshman) on birth control and STD prevention. I told the women that if a guy said that condoms didn't fit him the proper response is "why, are you too small?" I've had to say it myself to men, and it never fails to work
Edited to answer question re: STD's in pregnancy. I always found that handouts worked well so ppl could follow along w/o taking notes. You could list the STD's and then what complications they caused, both during pregnancy and in childbirth... maybe put the life threatening complications in bold. Make sure they also tell what kind of treatment or complication prophylaxis is safe during pregnancy too, and at what stage it would be implemented.