I recommend XTreme Monkey cast iron kettlebells and they can be ordered online at The Treadmill Factory.

Kettlebell sizes - women

I recommend women buy one 8kg kettlebell, one 12kg kettlebell and one 16kg kettlebell.

Kettlebell sizes - men

I recommend men buy one  12kg kettlebell, one 16kg kettlebell and one 20kg kettlebell.