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

Kettlebell sizes - women

I recommend women under 60 years of age buy one 8kg kettlebell, one 12kg kettlebell and one 16kg kettlebell.

I recommend women 60+ buy one 6kg kettlebell in addition to 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.