Photographing Glass
The real key to getting the best light for a particular subject is to pay close attention to both the light location and how you diffuse the light. There is an infinte range of possible images of a single subject by just varying the light sources. The best light sources are usually doubly diffused and often cleverly crafted to suit the specific needs of a particular photograph.
To create a visbile reflection on the bottle I have used a black back drop and placed my white diffuser to right of the bottle and slightly behind it. The flash, triggered by a Canon ST-E2 infared trigger and set to 1/8 power is on a stand behind the diffuser. I have adjusted the bottle and flash position so the reflection of the light is visible in the flat surface on the side of this triangular bottle.
Here I have placed my diffuser directly behind the bottle and the flash zoomed to a narrow beam behind it. Exposure is set for the surface of the diffuser which is very bright, so the flash set to 1/128 power to allow an f/8 aperture.
The cross in the light pattern is created by the fresnel lens in the flash at close range. That cross pattern is less than ideal for most photographs so normally I would elimiate it by using double diffusion of my light source. That, however, substantially increases the complexity of the setup.
As a side note, the reason you pay good money for good quality softboxes is that they have an internal baffle specifically designed to smooth out any unevenness in the light source.