Male Anatomy (This article even covers penis size!–Not that it matters.)
Female and Male Sexual Anatomy and Physiology advice archives
The Sexually Transmitted Infection Quick Risk Assessment Sheet will give you basically what it says–telling you what various sexual activities may put you at risk for and how to deal with them.
STI advice from Scarleteen.
AIDS causes, statistics, prevention.
A lot of people are actually allergic to latex, which is the most commonly-used material for making condoms due to the fact that it is not porous. Here’s what to do if you are allergic to latex in order to practice safe sex.