Flux Pure Limiter.

Very clean and great sounding. You can even abuse it a bit by removing lookahead completely which makes it clip slightly before going into limiting. The advanced release setting allows you to set a maximum (theoretical target) release time and a minimum release time. To use an oxymoronic description: an automatic release with manual control. The velocity parameter controls the speed at which the limiter can adjust between these two settings. It also features a HPF and LPF in the sidechain of the release which gives you more control over the unavoidable dynamic artifacts caused by the release in any limiter when you're pushing the envelope.

Sonnox Oxford Limiter.

Logic Pro Bitcrusher (for clipping): 24 bit mode, no drive, 1 x oversampling, straight clipping shape, lower the clip ceiling according to taste.

EDIT: Today I use FabFilter Pro-L, which is currently one of the best allround digital limiters IMO. August 2012.