I have used Access Diagnostics a couple of times to order OPKs. They also sell HPTs, Personas, pre-seed and other stuff useful for TTC-ers. The prices are good, and delivery is pretty fast.
If you're thinking of ordering from them, entering the coupon code AUT 001 will get you a 5% discount on your order.
Once you've ordered from them you can request a username/password for their site which then gives you a 5% discount on your subsequent orders.
I hope this is useful to some of you ladies
Hugs,
Artoo.