Warhammer has some detail on falling afoul of the legal system and dealing with your day in court - in the Marienburg: Sold Down The River setting book for 1st edition and in the WFRP Companion for 2nd Edition.  Since you're usually playing everyday schmoes and dealing with a medieval culture paranoid about infiltration by Chaos, it was certainly something that came up a lot in my group's games.  (I even started out an adventure with the PCs being arrested and having to stand trial in court...)

Ars Magica seemed pretty concerned about different types of law, too, from dealing with secular nobles and the Church to hermetic law within the Order of Hermes.  It was presented in 3rd and 4th editions as something that the PCs would probably have to deal with fairly often - the act of magi operating a Covenant in itself, much less traveling abroad to collect vis or seek regio or whatever, required dealing with the laws of the land so as not to tick anybody off and spark a Crusade.

Oh, and I almost forgot: I don't recall how much of an actual legal system it presented, but the old Ghostbusters RPG had tables for dealing with bureaucracies of all kinds, from the EPA to the IRS.  What I wouldn't do to have copies of those tables again...

In my current StarCluster IRC game, which Marco is in, the culture the PCs have come into is an extremely rich, extraordinarily high tech world which is ruled by a cloned Queen. The basis for all government, law, and society is trust - the People must trust the government, and the government must trust the People. There is no government if there is no trust - loss of trust will bring down a government. Extraordinary license is given those who earn that trust, and violation of trust is the ultimate crime and societal wrong.

It is legal, and considered morally right, to kill the Queen if she does not keep the trust of the People. If a Queen dies, the various clones - each backed by a Major House - appoint a Champion or Champions who can do what they like so long as the People see their actions as right and proper. If the Champions screw up, the claimant pays - either by giving up the claim and leaving, or by putting her head on the block. The weaker claimants flee the world and give up any ambition to rule. the stronger claimants vie to have the last Champion standing. When there is only one claimant left, she is Revealed as the Heir, and is eventually crowned.

For example, in the current situation, the strongest claimant was behind the assassination, but less than a day later repudiated her Champions and fled the world because her Champions bungled the assassination and bystanders were harmed. The maneuver was seen as awkward, thus the claimant excercised poor judgement, thus she was not worthy of being Queen. The ex-Champions, however, will not be tried for the assassination - all responsibility for the acts of the Champions is taken by the claimant.

In the meantime, between the death of the old Queen and the crowning of the Heir, there is no higher world government.

The PCs have been named Champions of one of the claimants, and will not suffer consequences for their actions, however - if they choose wrongly, screw up, look bad, or are caught cheating - their claimant will suffer the ultimate price. The fact that their claimant holds positions that they passionately believe in, and the fact that they will materially benefit from this association of their claimant is the one left standing, makes it all very interesting.

-clash

Dang, everyone else beat me to the good ones.  I've only ever used the legal systems extensively in Shadowrun, City State of the Invincible Overlord, and Tekumel.  As others noted earlier, the designers in those games did a good job of integrating the legal system with the rest of the game so that it just seemed to flow rather than impede play.

Having Lone Star always on the mind of runners kept some of them from doing some really boneheaded things (not always though) and in CSOIO I actually ran a game around the players getting tossed into jail for insulting a noble.  Since the Wraith Overlord supplement lists the lower levels of the jail it made for a great sewer break out adventure.

I agree with the OP, working the law into games can be a real benefit.