Most popular locales are Upper Fells, Inner Harbour, Mt Vernon, Canton, and Middle East (area surrounding hospital).
Upper Fells: row homes – big, spacious, cheap if split. Usually 2-4 person. Fun neighborhood, but wouldn't recommend living immediately off Broadway d/t crime. Also some places right next to neighbourhood bars can be quite loud. Historic row homes can be more rustic (ex: no AC), pricier ones can be fully gutted and renovated with new trappings. Lived here for 3 years and enjoyed it!
Lower Fells (aka: Fells proper): closest to nightlife, very similar to Upper Fells, but add a 10 min walk. Waterfront places here are $$$ but gorgeous. Apartments include Union Wharf and the Crescent.
Inner Harbour: luxe, kinda sterile, Whole Foods + Lululemon, easily the most pricey $$$. Apartments include Spinnaker Bay, the Liberty, Promenade, 1405 Point.
Mt Vernon: historic, chic, artsy, a little further away. Hub for LGBT scene. You'll have to drive or take the shuttle if you live here. Popular apartments include the Park street complexes, Symphony, and Waterloo.
Patterson Park: usually refers to area north of the park. Row houses, usually the cheapest options. Be aware the further north you get, the rougher the area tends to be. Right off the park is usually safe, though.
Canton: quiet, safe, residential – similar housing to Upper Fells but a little quieter. Southeast to campus – either a heck of a walk (25+ min) or drive. Can potentially hitch employee shuttle from Patterson Park area. Closest to Safeway and Target, but you'll still need a car to get there!
Middle East/Mt Washington/???: idk what to call this neighbourhood, but it's the area immediately surrounding JHMI. Apartments include 929 (to the north) and Jefferson Square (to the south). A few row houses also available. Not the glitziest or nicest area, but ~5 min or less walk to campus!
Edit: concur with
@efle – lived in 929 my first year. Was great to meet everyone, but was paying basically 1k for a cube in a largely undeveloped region of campus. Dorm-esque feel, both in pros and cons. Moved here because none of my roommates knew the area or could tour places before moving.
I think it's missing ~4 people – know at least of an additional derm and ENT person. Students can elect to include/exclude their Match results, though I'd say vast majority of people have their results up there.