I use Prochannel Concrete Limiter on the master, sometimes Ozone 6 Limiter
Tracks... Concrete limiter

Slate fg-x here.

I've already mentioned LimiterNo,6 as being my favorite, but I also use the Concrete Limiter, TB Barricade, T-Racks Brickwall, and fab Filter Pro-L. There are so many good ones out there and you certainly don't have to spend a thing to get great quality. I sent in a donation for LimiterNo.6 since I use it the most.

The Cakewalk Concrete Limiter prochannel plugin works real nice, particularly with it's "moar bass" switch. Have to buy it extra, of course, but it seems to do pretty well and is easy to use.

When I want my rock tunes to be LOUD I use Slate FG-X. Otherwise on the master I use Ozone 5.

I have the Ozone limiter, Slate's FG-X, and Sonnox's limiter as well. I enjoy dynamics in music so I'm not typically using the limiter to get any loudness war average levels. I have to say that the Sonnox level can squeeze a lot of level out of the signal without distorting too much. The Ozone limiter doesn't seem to able to keep up with the Sonnox limiter in that regard. That being said, you can get a little more level out of the Ozone limiter with some adjustments of the Character, Intelligent Release styles etc... I haven't tried the FG-X extensively as I need to get a little comfortable with some of its controls.
 
In any case, I don't push my limiters that hard so all of those limiters handle the job I need quite well.

Waves L3-16. The priority function is something not to pass up. The myriad of Release characteristics is divine as well. The EQ function of the L3-16 is Linear-Phase and quite good for subtle/broad adjustments. 

I've got a couple of limiters but since getting Pro-L I'm sticking to that, for no other reason than I like all of the FabFilter stuff, with their great GUI and excellent video tutorials.

No one has mentioned really the ultimate limiter yet.
 
 
 
 
 
 
 
 
 
 
 
 
PSP Xenon
 
 
 
More control than most limiters especially how transients can sound.
 
 
Watch out, some limiters are only good in certain genres. Waves being one of them. (L1 and L2, have not used L3 so not sure on that one) They tend to crunch a bit. No good for pure transparent sound. Might be good for rock but we don't always do rock.
 
 
 
 
Boost 11 is the worst limiter ever invented. Even doing light duties just catching peaks it distorts the mix to my ears.  Don't ruin your fantastic mix as Bit puts it through any old limiter you have lying around. You are doing yourself a real disservice.
 
 
 
 
 
It is the final link in the chain. Be careful. Maintain mix integrity.
 
 
 
It is not cheap but you get what you pay for.

Xenon is sold on KVR all the time for less the $100...