Always a good place to start is
rent.com. I would try and start around the zipcode 21201 (which is the hospitals zipcode).
Here are some places that are really close to the campus (within walking distance) since it can be hard to figure it out looking at a map.
The Sail Cloth Factory
The Redwood - this would be one I would seriously consider if you can afford it (real nice)
The Malboro/Redwood Square - I lived in Redwood Square during first year. I really disliked the management and had a lot of problems while living there (a dumptruck that would come at 3am on several mornings ... and was so loud it woke me up, the lady downstairs that must have had a marching band playing all the time, another lady that almost assaulted me in the hallway and finally it just didn't seem secure - some of the homeless people from the streets would roam the halls)
The Atrium - a little further but the rent is a little cheaper. This is close to Lexington Market so it could be considered not safe but, I lived there during second year and really liked it although the management here wasn't all that great either ... lots of changing of employees.
The Greenhouse
I also lived at Spinnaker Bay which is like a mile from campus. VERY, VERY nice apartment complex but extremely expensive. My husband and I wanted to live somewhere nice in the city before we left and decided we could splurge for a year (not a great idea b/c it came back to bite us in the butt) but, it was definitely worth it.
Also, UMB (which is all the professional schools) puts together a very helpful website that gives links to all the places around the campus. Be careful though b/c some of these places are rather far away (won't have an asterick).
This might actually be a better place to start. This will also allow you to view ads for roomates (in some of the townhouses or apartments around the area).
http://www.housing.umaryland.edu/
http://www.housing.umaryland.edu/commercial.cfm is the apartment listings