FOR SINGAPORE:
I have come across two stores that sell classical string instruments, including guitars, violins, violas, cellos and so on. I am not string player, so I don't know about quality, but both stores look pretty credible.
Maestro Guitars at Esplanade Singaporehttp://www.maestroguitars.com/Handcrafted instruments, salespeople commended for good knowledge of the available instruments.
Looks like a very classy, professional shop that those who don't play wouldn't want to enter for fun.
Now and then, you would see a master crafting the body of a violin in the window of his workshop.
Music Essentials at Meridien Shopping Centre, Concorde Hotelhttp://www.musicessentials.net/One of the best places for music books in Singapore, which some of you might still find inadequate.
Not as classy, but the salespersons are rather friendly, especially when it comes to selling string instruments.
I think some of them are players too. There are violins hanging overhead in the store.
Of course there is Yamaha as well, but I get the impression that Yamaha salespeople don't really know their products. There are young newbies who only recommend based on budgets.
If you want some cool electric/electronic instruments and mixers etc, you might want to check this out:
CityMusic at Peace Centrehttp://www.citymusic.com.sg/Located in a really old building, this store is rather popular among those who work with electric guitars, keyboards and drums. I don't really know what kind of stuff it sells, but I managed to get my Zoom H2 sound recorder and KDM-2 metronome there.