So one thing I plan on giving all my players in an upcoming campaign is an improved critical hit effect.
It is a homebrew/Rifts/Starcraft campaign. I have some shooty, some melee, some AoE, and some Psi powers going on.

Anything we can do for these guys would be cool. I'm going to build a bunch of effects appropriate for each character, and then let them pick, but I need some suggestions.

The guy playing the Reaper is all about speed. Fast movement, lots of attacks per round, shoots on the move, etc. His base crit effect gives him extra damage on that hit, and extra damage on his next hit. He gets bonus attacks per round the more he focuses on one target.
The guy playing a Marine is also focus fire inspired, but he gets a stacking damage effect the more he hits a single target.
The gal playing a Zealot is twin weapon focused and gets extra attacks when criting already.
The lady playing a firebat sprays twin flamethrowers, and currently doesn't have a crit effect. I was thinking a burn effect over a few turns would work well.
And the fellow playing a Maurader fires grenades and special grenades and does demolition work. Currently no crit effect either.

So, suggest me a bunch of critical hit effects that you're fond of, and I'll see what I can come up with.