A Limiter is a dynamic processor very similar to a compressor but with a much higher compression ratio. A Limiter is used to ensure that the output level never exceeds a specified maximum gain level. It is very useful when you need to increase the overall loudness level but don't want the audio to clip.

Neutron from iZotope is a mixing channel strip with EQ, Compressor, Exciter, Transient Shaper and Limiter. The presets and Track Assistant quickly gives you a good starting point and the Masking Meter helps to avoid frequency collisions.

FabFilter Pro-L is the most impressive limiter I have tried yet. It  has a unique real-time level display, output and level meters with inter-sample peak detection and K-system support. 

Price: € 169

Frontier from D16 Group is an easy to use mixing/mastering limiter with excellent sound quality. It features automatic output gain make up, configurable control input, controlable release charecteristics and optional soft clip. 

Price: Free for registered D16 Group users.