I see a lot of threads posted asking questions about where to get a chip, who makes the best one, etc. etc. Maybe this will answer a few questions...
First off, software upgrades should be added as the finishing touch to upgrades, not at the start. Any mods you plan on adding to your car, should be done prior to buying software. Exhaust, CAI, injectors, cams, MAF or any other engine modification should be done prior to adding software. Why? Because software takes the components you have, and makes decisions based on that. Example: You buy a chip, and then add a CAI. You are doing yourself little good, as the chip won't necessarily take the added CFM your new CAI is adding into consideration when maping your fuel curve.
Where should you purchase a chip? Not ebay! As ebay is sometimes a reliable source, it's not worth the risk in this instance as chips are the epicenter of one's engine management system. I've heard horror stories of a chip purchased from ebay (believed to be a proper Dinan chip for an e36) ruining one's ECU as it did not contain the proper proms.
Active Autowerke, Bavrian Auto, TurnerMotorsport, and DinanBMW are all reputable sources for software upgrades, as most of the aforementioned use a similar prom.
I have an Active Autowerke chip. I chose them, because they were willing to custom tailor a chip to maximize all the various components I now have. Dinan and Turner both said they couldn't or wouldn't do that. Karl Hugh is an absolute mastermind, and was featured in the April '05 issue of Bimmer Magazine (if you don't read it, you should) for sucessfully putting together a supercharged e46 ///M3. His knowledge is second to none, and their customer service is impeccable. Karl asked me every question I thought he would, and several I wasn't expecting. For a decent chunk of money, they were to burn a few different chips for me to test on the dyno, and report back the results. He was very thorough, and this was apparent with each chip I tried. "Tuning a car from several hundred miles away is difficult ," Karl said, but he is able to do it nonetheless.
If you want top notch customer service and a product you can count on, look to AA, they are worth every penny.