These commands display the fps, choke, loss, in/out transfer rate etc. the graph 3 is the best one. I personally prefer cl_showfps 1 as given above, but a lot of people use the net_graph.
You can change the position of the net graph by using net_graphpos or net_graph_pos (can't remember, but it will appear automagically in the console I guess) and enter the value 1, 2 or 3 for different positions.