You mentioned that you're in college...If you can't figure out what size condom to buy and you've never used them before (this may not apply to you because you've already had sex) you might consider trying your student health center (as long as you're not attending a religious school or a small college with fewer resources). They often offer free condoms and you can at least try out the kinds they have there to see if you like one. I was involved in a program in my dorm called Student Health Advocates, which basically meant that I learned CPR/first aid, had OTC medicine for people with headaches/colds, and gave out free condoms to anyone who wanted them at (almost) any time of day. Maybe your school has something similar. Another good place to buy condoms is from reputable sex toy shops (I go to Good Vibrations out here in Northern California). They sell condoms individually, so my boyfriend and I got a few different ones before we found our favorite.
From personal experience, don't start buying condoms in bulk until you know that brand works for you and your partner. Susan is right that the length of the penis doesn't matter (every condom I've ever tried has been long enough) but when we were first buying condoms my boyfriend's girth was really an issue. His penis isn't any longer than average, so I guess we didn't think it would be a problem. At first I thought he was just trying to impress me by needing a bigger condom, but then I tried to roll one on him when he was hard and it literally would not roll down without a fight. He was lubed and everything! We tried a few of them (just regular Trojans) and they were all like that. Part of my health advocate training was teaching people how to use condoms correctly, so it wasn't user error...anyway once we got it on he couldn't maintain a full erection because it was too tight. But you could barely even tell that a condom was on him, the latex was stretched so tight it was clear. We just ended up laughing about it and buying wider ones. Those worked fine, so maybe some guys are more sensitive to tight squeezing than others if it isn't really a size issue.
OK so I rambled, but the moral of the story was to start with a 10-pack or less and work your way up.
