My longest is from just over the Half Way line.
If you notice when the opposition are attacking you in your own half, their keeper stands on the 18, and continues to do so until you pass into the oppositions half. If you have someone with a very powerful and accurate shot (mine's was a "promising player" called Titanes-99 in both shot power and accuracy), and sprint over the half way line, shoot straight away.
It's hard to do, i've had one thats hit the bar, one where Seaman made an amazing save, One that went in, and the others all just went anywhere and everwhere.
Another tactic i use to set up long shots is at corners. Play a short one, then with the player it goes to get him to face diagonally away from the corner flag (that u have just played the short from) and play a thru ball (or chipped thru ball can work a treat too) backwards. About 5/10 times one of your players will run ontoit, setting yourself up for a good 25 yarder. However it can get deflected off the defenders very easily. I've hit the bar with a cracker with Gerrard this way from about 30-35 yards, scored a mint volley with Zidane and scored a very lucky one with Viera. The rest were all just shite.lol
Anyway, try it out, i'm sure some of you already have. Let me know what you think.