I'm dealing with bruised ribs right now. I was doing a non-traditional pin (in our syllabus anyway), holding uke down with my side while arm-barring him while leading class. I didn't have it in tight, because I was showing a newbie how to do the pin. While I was explaing, the uke based up to his knees and came up into my ribs. Ouch! They still hurt a couple of weeks later, but I can at least do ukemi now (it hurts way worse when I sneeze than when I take a breakfall, go figure?) I broke my little toe in a demonstration, it got caught between tatami. That was a [censored], especially because I didn't want to look like a wimp jumping around the mat. So I pretended that it didn't happen, and proceeded to limp around for the next month and a half or so.
When studying for my nikyu test, I was working with a relatively new student on keri waza, which involves a higher level of ukemi than this student had. I didn't feel comfortable about throwing him, but one of our sensei's was right there and I was going slow. When I threw this poor guy, he came down on his collar bone, luckily didn't break it but he couldn't roll for months. Considering how big this guy is though, I think that he got very lucky that he didn't break it. That's the worst injury I've seen in the dojo, and I'm greatful for that.