http://www.grabone.co.nz/home/skinny-mobile/
Update: other deals too!

$50 for $100 credit
$20 for $40 credit
$99 for 7.2mbps USB Modem (worth $49) with $100 credit 
$149 for Nokia C2-01 (worth $69) with $160 credit
$199 for Nokia X3 (worth $99) with $210 credit
$209 for Huawei Sonic (worth $139) with $210 credit