Honestly, you would be taking shots in the dark and probably wasting money by purchasing parts at this point, especially due to the fact that when you truly do have a fried logic board, there is really only one part number to purchase -- the logic board -- and as Apple has probably informed you, that's not cheap.
The best "bang for the buck" with salvaging water-damaged MacBooks, I've found, is to pull the memory and make sure it doesn't have any corrosion on it. If it does, clean it off with q-tips dipped in rubbing alcohol, and then test the memory slots by powering on with one slot empty, and then try with the other slot empty. Better yet, if you have known-good RAM, try that. I would try to reset the PRAM as well (connected to AC and with the power off, hold in the power button until you hear a tone and see the sleep light flashing).
I have ended up with many working MacBooks after simply doing the above with the RAM. Apple is generally too lazy to bother testing it, and "liquid damage" is the magic phrase that make them back off and tell you it's your problem and not theirs, so I'd suggest not saying it unless you absolutely know that's what caused the issue.
Those who have more experience with unibody laptops than I do may be able to suggest some specifics, i.e. is replacing the DC-in ever an effective step, such as it is in other models?