Its perfectly fine to mix different brands of clubs in your bag. In fact, I tend to question anyone who doesn't because it tells me they have blind loyalty to a particular manufaturer probably to the determent of their game. If you don't believe me, visit the golf channel's website or pick up a copy of Golf Digest and read the "What's In Their Bag" section. The pros typically mix and match depending on what works for them after trying probably dozens of combinations of brand, loft, lie, shaft, and grip. That is unless they have a big money contract with a particular brand like Tiger with Nike or Phil with Titleist.
So, demo lots of clubs and see what works for your swing. Personally, I have my clubs custom built for me using component heads, fitted shafts, and grips. Golfsmith is a good place for that or any local clubfitter. To be honest, you end up paying less than Callaway, Ping, Taylor Made, or Titleist and receive a product that works as good or better. Not to say that those products are bad, but they cost big bucks $$$$. I don't know about you, but my game doesn't warrant a $400 Driver or $200 Fairway Wood!
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If you grip it and rip it, then be prepared to go find it.