you can put the zip code from where you'll be watching in here
http://mlb.mlb.com/mlb/subscriptions/index.jsp#blackout
and it will tell you what teams are blacked out in that market.
I have the mlb radio app on my phone so I can listen to games (the radio feed isn't blacked out) and you can often listen to local announcers or the opposing team's announcers, which is fun.
I've been wanting to cancel my cable service, and looked into mlb.tv via the Roku box (which I already have) but decided against it since my local team is blacked out.