I use different mixers for different situations. I always run a balanced signal (Tip Ring Sleeve TRS - 1/4" to XLR) to my powered speakers.
Sonar VS-100... Bought on blowout at Best Buy for $190... New $499 to $599
---Built in SD Recorder/player
---2 XLR and 2 Stereo In
---Built in FX
This is the main mixer I use for our duo shows.
Edirol M-10DX... $150
---Back up mixer... always in the van just in case!
---Great Little Mixer
http://www.youtube.com/watch?v=t1KaScw46VYMackie DFX-12... $200 back in the day... I got it in 1999 or 2000
---For bigger gigs
---12 years old and still going strong
Yamaha n12 in my home studio
Yamaha MG10/2... Bought used for $50
Looking forward to the new Yamaha MGP16x for $799
---16-input 4-bus mixer
---8 channels of single-knob compression
---Dual FX - One SPX and One REV-X
---iPod connectivity - Steel chassis - internal power supply
It's funny how we spend so much on a great keyboard and run the sound through a $100 mixer.