Journal of Young Investigators

JYI gives new meaning to "peer review". This is a journal entirely by undergraduates. Undergraduates are the only allowed authors, undergraduates do all the reviewing, undergraduates are the editors, etc.
The coverage is extensive, addressing  topics from detecting bioterrorist bacteria to electroshock treatments, jellyfish poisonings to extrasolar planets. All STEM fields and even social sciences are addressed. It seems like many of the publications are capstone theses reviewing a subject with a few research projects mixed in, and the writing is higher quality than many of the "third-tier" traditional journals. If you are looking for a foothold to learn about science publishing, or a place to publish that awesome essay you just finished, you should definitely check them out.