What varieties of potato would be good for making chips / french fries that can be cooked in a deep fryer to give a nice golden crunch on the outside, but still be nice and fluffy in the middle?
The potato is probably not as important as the method. Simply frying them will not get you the fry you want. Basically you boil them, then double fry them. Here are the steps for The Perfect French Fry:
2 pounds russet potatoes (about 4 large), peeled and cut into 1/4-inch by 1/4-inch fries (keep potatoes stored in a bowl of water)
2 tablespoons distilled white vinegar
2 quarts peanut oil
Place potatoes and vinegar in saucepan and add 2 quarts of water and 2 tablespoons of salt. Bring to a boil over high heat. Boil for 10 minutes. Potatoes should be fully tender, but not falling apart. Drain and spread on paper towel-lined rimmed baking sheet. Allow to dry for five minutes.
Meanwhile, heat oil in 5-quart Dutch oven or large wok over high heat to 400°F. Add 1/3 of fries to oil (oil temperature should drop to around 360°F). Cook for 50 seconds, agitating occasionally with wire mesh spider, then remove to second paper-towel lined rimmed baking sheet. Repeat with remaining potatoes (working in two more batches), allowing oil to return to 400°F after each addition. Allow potatoes to cool to room temperature, about 30 minutes. Continue with step 3, or for best results, freeze potatoes at least over night, or up to 2 months.
Return oil to 400°F over high heat. Fry half of potatoes until crisp and light golden brown, about 3 1/2 minutes, adjusting heat to maintain at around 360°F. Drain in a bowl lined with paper towels and season immediately with kosher salt. Cooked fries can be kept hot and crisp on a wire rack set on a sheet tray in a 200°F oven while second batch is cooked. Serve immediately.
Worth reading is also the science behind the perfect fries.
Looks like the preferred potato for the Netherlands and Belgium is Bintje, that one is being mentioned in various places. It also seems that a slightly floury potato gives better results than a waxy one.