I play mostly acoustic materal with some rock thrown in occasionally. I second the vote for Ozone, however if my project master doesn't need mastering the T-Racks limiter on the end of the chain set up properly does the trick. I also find myself using it for guitars sometimes.
If you play hiphop I think that the T-Racks limiter is a good choice and will really 'pump it up'. The limiter you can get for the PC is probably just as good or better though.