hello
i'm looking for a good sidechain plug in, with a low Cpu usage, what do you recommend?

for House , Tech house Style
most for Hihats and Drums loop, to sidechain with bass & kick

Thanks

Stillwell The Rocket?

http://www.stillwellaudio.com/?page_id=68

EDIT: or Xfer LFOtool. Technically no sidechaining but it sounds the same:

http://www.youtube.com/watch?v=94MRdk9zTHw

Vengeance Multiband Sidechain or, as manducator mentioned, Xfer LFO Tool to get the same ducking effect (and a LOT more) w/o sidechain.

http://www.youtube.com/watch?v=8aoMb_yKg14

FYI - the Vengeance MBSC requires an eLicenser dongle.

The vengeance one is twin band and my preferred recommendation. It's just superb. It does in seconds what finetuning of comps and sidechain sources would normally take. Love it to bits.

Agreed 100%. Also, it should be mentioned that it works with or without an actual sidechain input. When using it without an input assigned, it simply triggers the compression on every beat using an internal source. Also, when using an external input, you can select between an audio source, or MIDI notes, which allows you to create custom sidechain rhythms/patterns very easily.

Depending on your daw you probably have a decent compressor with SC already. For SC they are usually good enough.

I think the Vengeance MBSC looks good, but if you can't afford it check out cable guys, they do volume shaper 3 which will let you fine tune your pumping, though it's not at as sophisticated as MBSC.
I'd also recomend softube FET or NI VC 76

features

https://www.youtube.com/watch?v=lsmKItuZxXQ

Please feel free to demo SD-GATE87 and SD-COMP87 which feature a sidechain input.
The sidechain signal (or the original one when the sidechain input is not used) can be filtered to make a specific frequency range trigger the effect (which can be practical if a complex loop is used as reference).

LFO Tool can be found at http://www.xferrecords.com and has completely changed sidechaining for me.

You have complete control over depth and shape of audio removed, and it's amazing how small changes sculpting the sidechain have a big effect on the groove of a track.

And at $50 it is a no brainer. Another huge plus with LFO Tool is the developer, Steve Duda. I've had Steve return support emails within minutes. Steve is absolutely top notch.

The Vengeance MBS is an awesome plugin... that is until you need to change your latency settings in Ableton, then all the triggering goes out of time. There is a compensation control but who has the time or patience to go through 15 or 20 tracks and adjust this for each instance you use??? Are people experiencing this on other DAWs?

TAL Filter II can also be used to "fake sidechain", just assign the modulation to volume.

The Glue is a circuit-modeled SSL bus compressor plugin with an external sidechain. Pretty much exactly what you are looking for.

FabFilter C (SC)

The Glue does sound great in SC, as does Fxpansion's bus comp.

Not low on cpu, but Molot.