I'm experiencing slow flash recycle times. What can I do to troubleshoot or speed up the flash? I'm using a Nikon D90 with an SB700.
There are a few primary influences of cycle speed:
You'll experience the most inconsistent recharge rates with alkaline batteries. You'll want to make sure you are using high quality batteries which can drastically improve your recharge rate and consistency throughout their charge. There is a good discussion on battery selection here.
Too often I find people using a higher power flash setting than necessary. With the D90, you should be stepping up to 200-400 ISO to give the flash a break.
The SB700 knows to slow down if it starts to get too hot. If you're using the flash in warm temperatures or rapidly flashing at high power, the flash will begin to limit itself. This can become permanent if the flash has been brought to extreme temperatures.
There have been multiple reports of NiZn batteries permanently damaging flashes. I hope you didn't use those...
If there is a short in the flash somewhere, then the camera may be getting very hot in a single flash, triggering the governor that slows it down.