BioWare has stated that when you finish Mass Effect 3, Commander Shepard's tale will come to an end. The Mass Effect trilogy has been all about Shepard, and any future games in the universe will focus on new characters. However, BioWare has suggested it may be a good idea to keep the Mass Effect 3 saves around once you finish the game, but did not elaborate further. What this means could be anyone's guess, but it is likely future Mass Effect games could pull some elements from the end of Mass Effect 3. BioWare still has not said there will be future Mass Effect games, but has not ruled out the possibility either. With the studio saying "it wouldn't be a bad idea" to keep the Mass Effect 3 saves, one can speculate BioWare is thinking of new ideas set in the universe.
Mass Effect 3 launches on March 6th for the PC, PS3, and 360. BioWare wants gamers to be satisified with the ending of it, and all the choices we have made in the first two games will have an impact in the third.