If we are talking about single playthroughs, then some RPGs reach 100+ hours, as long as you go for sidemissions etc.
Longer than that (always for single games, not starting new) you would have to look for either open ended strategy/sims or MMO games.

For example.
The game Colonial Conquest by SSI (old game), a single game could take more than 100 hours, especially if you played on harder difficulty and/or with some additional human players.
Some of the Evochron games can reach more than 100 hours as can the X series.
Personal record for single game I would say a large winSPMBT PBEM campaign, with each battle needing between a week and a month on average to finish (few hours each day), which means the campaign/war getting to half a year or a year to finish.

Empire Deluxe can also take many many hours for a single battle, at least on large maps.

Carrier Command, if you play a strategic game and don't a shortcut, it can take several days, if you use time compression, else weeks.

And of course the absolutely monster Elite Frontier where if you don't use Warp, you might as well just write your will for your grandchildren to write their will etc for several generations till your ship reaches just one of the out of the system planets.
:p