There are 8 total companions in the base game. 2 of them are evil, so the remaining 6 are either good or neutral. The coolest of the companions is Fawkes, who is also good, and you get him as part of the story later in the game. However, for the rest, the following Wiki page lists them, and clicking their names will give you a page telling you how to get them.

http://fallout.wikia.com/wiki/Fallout_3_companions