http://www.starfall.com/n/level-a/learn-to-read/load.htm?f
http://www.fisher-price.com/fp.aspx?st=10&e=gamesLanding&mcat=game_infant,game_toddler,game_preschool&site=us
http://games.funschool.com/games.php?level=1
http://www.noggin.com/games/index.php
http://www.primarygames.com/games.htm
http://www.uptoten.com/kids/uptoten-features-firstvisit-home.html
My daughter has speech development problems as well. Her favorite sites are fisher price, pbs, and star falls. These also provide games to say and repeat with her...more educational that is. Star fall is great. Although is it primarily to help learn to read, you can also use it for speech. Along with this, you can begin to teach them how to get comfortable with the computer.
You will also want to read as many books as possible, and surround him with other children.
Check on free speech development programs within your community. You should have them. Call the Health Dept and see what they have or suggest.