We Farang need to start looking for alternatives to the madness at Pantip and MBK. I agree that MungkokGadget is a relief from the endless rows of 'same-same' stores in Pantip, but most Western currencies have lost ground against the baht since this thread was started. You need to run a few of these numbers through xe.com and ask yourself if you are really getting a 'bargain' ...
For everything other than headphones/headphones amps, I would check out stores like Piyanas and Conice Electronics - you can find their locations from their respective web sites. Be wary of 'too-good-to-be-true' prices on anything from vendors who aren't authorised dealers - you will have zero warranty if the thing fails. Note also that Thailand has 230V mains power - fine for those of us from Australia and some other parts of Asia - not so for US shoppers. From memory, electronics imported into Thailand attract 7.5% import duty, speakers 15% and there is a VAT on top of that - can't say that I've seen too many shops outside the airport displaying a 'VAT Refund for Tourists' sign, but it may be an option if you do find one.
DACs@Piyanas (their headphones are overpriced - higher import duty than electronics)
(I would add that my last trip to Pantip was marred by a particularly unsavory suggestion from a pirate DVD vendor that I would like to see something that would get most of us jailed in our home countries (and extorted in Thailand ..). If confronted by one of these touts, just keep walking. Don't even bother expressing your disgust - water off a duck's back...... )