I've done some research and it seems like Baltimore County and Baltimore city are good, but is there anything closer to the Northern Virginia border in Maryland that has a good market for wholesaling?

BC is so rich in real estate that I'm surprised you wish to invest south of the border.  

Here is the link.http://www.meetup.com/SF-Bay-Area-Real-Estate-Investing-Club/@Jeff Pollackalso hosts a monthly meet-up in San Jose bordering Saratoga. 

Despite bordering a busy street and active railroad tracks, they sold for $222K - $248K each.

I think what you are looking for are neighborhoods right on the border between Montgomery County (Glenside) and Philly County. 

I use foremost for a long term rental across the border.

Lots of people do make money buying in the up and coming neighborhoods of Detroit (a more difficult strategy) and I personally don't own a property IN Detroit, but my entire portfolio is in the suburbs bordering Detroit. 

http://www.youtube.com/watch?v=M6qOtpNochU&feature=player_embedded

@Brian WertThat area is right on the border of the Trinity Vicinity neighborhood, which is a decent area in the city. 

“With the biggest trading partner being the US right on the border there, and their economy picking up, we see great opportunity,” he explains.