12 days in the south - Khao Lak and ....? Koh Phi Phi?

My husband and I will be in south Thailand for 12 days during our 2 month trip. We're planning to spend some time in Khao Lak, including a 3-day diving trip to the Similan Islands, where we will camp out in the park itself (a very cool trip offered by wicked diving in Khao Lak).
We're thinking about maybe visiting some other beaches/islands in the area.
Anyone have a suggestion of a scenic place which won't be completely overwhelmed with tourists at this time (obviously it's the high season so I'm not expecting to find any deserted beaches).
We might also be into doing a rock climbing course - I know this is possible at Railay Beach and Koh Phi Phi - anywhere else?
Is Koh Phi Phi really as horrible as it's been made out to be (in terms of hordes of tourists and overdeveloped beaches) or is there another side to the island that's actually worth visiting for people who prefer their vacations to be peaceful? Is there good snorkeling there?
I've looked at tezza's site already but I'd like to hear some more opinions and suggestions from people.

Thanks a lot!

Hey, when are you going to the Similans? I'll be on that trip Dec 24-26. :-)

Looking for a beautiful beach environment that won't be crowded and you can do some climbing? LAOLIANG ISLAND! Very similiar to the climbing around Railay but no crowds. great value private island resort. couple good local dive sites, snorkel from the beach. would highly recommend Laoliang over Railay during the high season.

Well for other people reading this, yeah, there is another side of PP for people who lie peace and good snorkelling - the laid back east coast.
There is more info on this at this http://tezza-thailandbeachesandislands.blogspot.com/ link.

There is also a link to LaoLiang's adventure company on the Hat Yao/Ko Libong/LaoaLiang page.