The most popular alternative bulb is the GE Link bulb. Roughly the same price as the hue lux bulbs but brighter, and available in more stores (in my experience.)
Usually $20 for the Philips vs $15 for the GE Link at 800 vs 750 Lumen :)
I only have the colored Hue lights and the white GE Link so far. I might buy a Lux just to see how it works.