JimboGames 501!
Your ultimate source for online flash and shockwave games. great games. all free.
http://www.jimbogames.com/501darts.html
Let's Play Darts!
Let's play darts!
http://www.onlineklas.nl/darts/darts.html
Smilie Darts
Instructions for the :)smilie java darts game, configurable for 1 or 2 players, 301, 501, 1001, and round the clock game options
http://www.smiliegames.com/darts/index.php3