Located in the heart of Rama 9, IT Mall, Fortune Town is one of my favorite places to buy proper IT equipment in Thailand. While a lot of shops in Bangkok sell outdated IT equipment, here you can nearly the latest stuff, to regular prices, from mobile phones, laptops, router to projectors and TV's that is the place to go.
Quality IT equipment in Bangkok is not that easy to find. Due to high import taxes as mentioned in the general shopping information, Thailand is not the place to buy modern electronic equipment, but at least here you find all quality equipment in one place.
You can get cheap good quality projector screens on the forth floor.