The April 2009 issue of Math Horizons credits "Felix Sun of the Albany Area Math Circle" with submitting a correct solution to a problem posed in their November 2008 issue. Although the problem was also successfully solved by three other submitters, the article made clear that Felix' submission stood out from the others because his solution took care to establish that the answer did not depend on a possibly unrealistic assumption.
Math Horizons is a publication of the Mathematical Association of America which features "problems for students at the undergraduate and (challenging) high school levels" in each issue. Some other math journals with problem sections include: the American Mathematical Monthly, Mathematics Magazine, the College Mathematics Journal, Crux Mathematicorum, the Harvard College Math Review, and the Pi Mu Epsilon Journal. All these journals encourage students to submit solutions to the problems and will publish the names and affiliations of those who submit correct solutions. Occasionally, the journals will also publish commentary highlighting particularly noteworthy aspects of a student's submission, as Math Horizons did with Felix' solution.
Local college and university libraries subscribe to most of these publications, and most are also available at special discounted student subsciption rates. Working on solving and writing up the problems in them is a great way to develop your skills in mathematical expository writing, as well as in perseverence and problem-solving, since these problems typically take a lot more time and effort to solve than typical contest problems.
Kudos to Felix!