Free software displays orders buying / selling for exchanges: Cryptsy, Bter, Coins-e.
Current pair for analysis: DOGE_BTC, LTC_BTC, DRK_BTC, VTC_BTC.
You can add pairs manually.
Upon detection of a difference between the exchanges rates (2%), the program displays a message.
Poll exchanges performed at startup and then every 10 seconds.
https://www.dropbox.com/s/13c5n44tc1oihj3/TradeHelper_1.1.zip - for windows
https://bitcointalk.org/index.php?topic=715620.0 - for developers [source]. Added BTC-E version
