BitLotto was likely the first blockchain-based "provably fair". It uses the transaction ID as the "ticket", and the results of a large government-run lottery to determine the winning numbers.
SatoshiDICE became a blockbuster (pun intended) method for online gambling. It uses the transaction ID to determine the "lucky number" (between 0 and 65,535). The secret used for determining that lucky number is revealed after the end of the day.
bitZino gets credit for coining the term "provably fair", and first launched an online blackjack game then followed it up first with video poker and then roulette as well. The game allows the user to change the client seed used for each play.
BitDice.com, SatoshiRoulette.com and others claim to be provably fair.
BitLotto and SatoshiDICE wagers can be verified by anyone at any time after the results are published in BitLotto's instance, and after each day's secret is published for SatsoshiDICE's instance. Proving that bitZino always computed the results correctly requires logging of the hash, the client seed, and also the way the hand was played -- so it is much more effort to verify unless there is automation but no automated solutions for verifying all wagers on bitZino have been made available.
Here's an article on what provably fair means: