you could gently compress the mix... then set a limiter to catch the peaks / pump up the volume (whatever you prefer)... best thing to do from my experience is to set the compression threshold so its at an average level for the mix... then actaully automate the levels going into the compressor (to even it out even more).. its takes a bit of time but its worth it if you want better results IMO....

then again you could just slap a limiter all over the mix and be done with it... :)