I've made a number of ginger beer sodas, and I like the ginger flavor to be hot and forward. You can tweak the sugar to make it more or less sweet and the ginger to make it more or less hot.

2 lbs fresh ginger, sliced (with or without the skin; with the skin results in a slightly darker brew but won't affect flavor)
5-15 cups cane sugar
1 whole lime, sliced into wheels
1 stick of cinnamon
1 tsp fresh allspice, crushed
1 tsp cream of tartar

Bring 5.5 gallons of water to a gentle boil, add the cream of tartar, ginger, cinnamon, allspice, and lime (a grain bag works great for easy removal). After 60 mins, cut the heat, remove the bag of spices/ginger/lime pieces, add the sugar, and stir until it is all dissolved. Cool, keg, and force carb.