Just try some Osram night racers, or the night breaker, or the Philips X-Treme Vision, or any high performance bulb.
Any of those will be a lot brighter than the stock ones. There really is no point asking which one is best as every one on the forum will give you a different answer.
Just try them and see which one you like best.
Personally i use the Night Racer plus, and i like it, it is very bright and has a very white light.
It is really worth upgrading all your bulbs to decent ones, as the stock ones are all pretty crap, I was amazed how much brighter my turn signals, brake light and headlight were after i used good quality bulbs in them.
If that is still not good enough for you you can get an HID kit, but that is a lot more faffing around and a lot more expensive.