So I bought a Hartke HA2500 bass amp head which outputs 250w at 4 ohms and 175w at 8 ohms. I also bought two Celestion 200w 8 ohm speakers. Now what would be the best way to wire these two speakers up?
14AWG speaker wire should handle the current if the cable run is short. 12AWG would be better. According to I=√(P/R) the amp will put about 8A into the speakers at full rated load. So ideally you want to use wire that can handle twice this without getting so warm that the insulation softens.

Edit: beat me to it.
That was a better explanation, though. It's good to know why instead of just "use this."

I've seen some bass cabs with 16 and that scares me. Someone mentioned a major company using 18 (!) recently but I don't know if that was verified.
I am european so I don't get your "gauges" and stuff so all I need to know is get a bunch of thick ass cables and I will be fine?