As a medical student your best resources for learning radiology are textbooks, notably Squire's classic text and Felson's red chest book. Paging through journals will probably give you a sense of what's hot in the research arena, although some of the material may be a little over your head as a 3rd year student. Some of it is over mine, and I'm a resident!
That being said, a good journal for junior people in radiology is Radiographics. They have lots of review articles covering fundamental topics.
The most respected journals for radiology overall are probably Radiology (the gray journal) and AJR. For interventional, check out JVIR.
Good luck!