Round four of our Summer Bikini Bracket ended last night and now we're down to the final four ladies in the contest. Jennifer Aniston and Jessica Alba are going head-to-head, while Bar Refaeli and Cindy Crawford are matched up in the battle of the swimsuit models. What's even more interesting is that in our top four we have two 20-somethings up against two amazing looking 40-year-old women. Voting in these pairs will be open until Monday at midnight, so make sure to log in and complete your bracket — and you'll be entered to win an iPhone! Official rules are here.