I spent a few days last year on the island of Ko Lanta. It's about 2 hours by car from Krabi. It was a great experience, there is tourism on the island but not so much that it's overrun by it. If you want a relaxing tropical island vacation, that's the place to go to. The only problem is that if you're going in August, it's going to be intolerably hot, so keep that in mind.

I spent 2 weeks in Koh Lak and loved it!!!

It's a small Island about 3 hours from Krabi by taxi.
Nothing very exciting going on there, but nice beaches, great little restaurants and not too many tourists.

I stayed at a place called 'The Andamania Beach Resort' (http://www.andamania.com/) and highly reccomend it.  It's a bit out of the way, but that's what I was looking for.

Enjoy your trip - Thailand is AMAZING!!!

Oded

Thailand
Groovy hotel chain in thailand www.reflections-thai.com/main.html
You have to (www.banyantree.com/en/bangkok/dining) for dinner or at least a drink – its a terrase in the clouds!
Best market in bangkok (in my opinion) is Chatuchak Market – and seriously allow several hours there!

Siem Reap
Stay at www.hoteldelapaixangkor.com or just stop in for a drink (tea or cocktail etc..) or book a suspended gazebo table for dinner) super plush!
I will try and find the details of my 4 hand massage place in Siem Reap – the jackpot is when u fine perfectly synchronised massagers, which is not easy..
The Blue Pumpkin (the one near the Old Market) is a super comfy place for juice and cool off with free internet.

I gotta run but I will be back online later if you want more..

Christopher

Hotel Victoria was very nice some time ago. Only a 5 min tuktuk ride from city center, or easily walkable, but nice to be outside the hot frenzy of the center. Calm fully equipped luxury wrapped in a soothing oriental style. Conveniently on the road to wats etc. Local business people like to meet you there.

The challenge with Thailand is that there are no longer any best kept secrets! I am serious. So many people try to relive the movie Beach that you will never be alone when it comes to tourists. But again you can put things into perspective. Phuket, Pattaya, and Ao Nang are pretty packed with package tourism, which can be the worst kind. But again Koh Phi Phi and Ko Samui are full of backpackers, which is not a lot better. It all also depends on which coast are you visiting.

Despite heavy tourism you might still find some ok spots at Ko Tao and Ko Phangan. Do not go during the full/half moon parties unless you are absolutely ready for it! But if you are at the Andaman Sea (guessing from Krabi) side you by far best bet would be (based on December 2009 personal experience) the small isolated island called Koh Jum. There is no proper road system, proper internet network or proper electricity. They all are coming gradually, but now it could be still the "best kept secret". Even the all mighty Lonely Planet still only gives a small note about it. And trust me, people go where LP tells them to go. And if you are in Krabi, don't miss Railey climbing and world-class snorkeling/diving spots in that area.

This website will explain enough about the small tiny island. 

http://www.kohjumonline.com/

But again seems like you have your plans quite open, so I would recommend to check Laos, Vietnam, and Malaysia (e.g. Perhentian Islands) in more detail. And if you are not looking for a beach, the North could offer you a totally different kind of Thailand experience. Also note that August can be a difficult time in many SE Asian places. 

Yes the Bayan Tree looks amazing!! Also we were going to stay at the hotel de la paix however the prices are outrageous!! I have no problem spending money for a nice hotel but 620 usd in Cambodia is a little much!! Thank you for all the advice I am writting it all down!

Why is it difficult in august? I am going at the worst time possible?

I already answered to this, but it seemed have lost in the bit space. Anyway here we go again.

August might not be the worst time, but it has few downsides.

Thailand: It's the rainy season. Tropical monsoons hit Thailand in early September. It probably worse in the Andaman sea than on the East coast.

Malaysia/Singapore: Huge forest fires are pretty common in Sumatra then. The "smaller" monsoon season hits the area about the same time. And then there is the Ramadan. It can be a challenge for tourists. This years it should be fro Aug 11th to Sep 9th. 

All around it's quite hot at that time. But I guess that's why many people go there. If you are prepared for the above, I think you will have a wonderful time. Plus most pros travel during the off-season. So chin up and get ready for an adventure...you are a traveller now :)