OnyX should take care of a lot of it, and also HALP with cleaning up your HD, like temporary files and what not. Good stuff.
I can tell you for certain right nao, that Photoshop sucks up the most memory - you know this, too. It's a heavy program. I won't tell which ones you should STOP USING while working in PS, just tell you what I gotta do with mine:
My Macbook Pro is like... a year old, with 700-somethin' GB HD blah blah blah, and I usually run Photoshop & iTunes. And sometimes, Skype. If I need to browse something on Chrome, I'll open it, then quit it when I'm done. This is mostly because of the heat - it makes a slight noise that sounds like LIFT OFF. So we joke and say my Mac has joined the Space Program, and I'll ask my friends if they'd like a shipment of Lunar dust. 8D Ah, I ramble...
Anyway! I am confident OnyX will take care of most of it! But your Mac is trying to let you know that you is WORKING A LOT OF STUFF and it's le tired. XD
(And WoW. Omg. You run that on its own, I hope. Such a processor HOG.)