Frogger is a classic!  Although the graphics and sound aren't as good as they were in the arcade version, the 2600 version of Frogger is still a lot of fun to play.  The game is pretty basic.  You are a frog trying to get from the bottom of the screen past cars and a river back to your home at the top of the screen.  You can move up, down, left and right.  The first few jumps forward are to cross a street with cars and trucks moving to the left and right.  There is a grassy patch (which has a snake on higher levels) on the other side of the street and then a river with logs, alligators and turtles moving left and right.  You jump on the logs, alligators and turtles and at the top of the screen, jump into 1 of the 5 spaces.  This is one of the most popular games for the Atari 2600, but since it's always been one of the most popular games, there are a lot of copies out there.  You can pick this one up for a good price just about any day of the week.