Here's a second thumbs-up for T K Foto Technic. I've been visiting Singapore two or three times a year for several years, and normally go to the stores quoted above. Last year, and early this year, I was looking for a tripod and ballhead. I found that there wasn't much choice and a lot of the gear didn't match the quality I wanted. Cathay had the ballhead I was after, but they didn't have the plates. I'd almost given up hope.
On my most recent visit I went to TK Foto for the first time. It was a very positive experience. They have good gear, good choice, and give good advice. I will be returning when I'm in Singapore next time. They're in Shaw Towers at the moment but the salesman, James Ng, told me they are moving to Funan shortly.
For what it's worth, here's my view of some of the other places. Cathay seem very geared up to selling - especially in the main shop. However, the assistants in the shop where they sell tripods and lighting gear try to be more helpful regarding your needs. Their prices seem to be on the higher side.
The guys in John 3:16 are a nice bunch - very friendly - and seem just as interested in photography as selling. I'm not sure of their opening times but on several occasions when I've visited, the shop has been closed. It's a small shop and they don't have the greatest selection of gear.
I would caution people new to Singapore against Sim Lim Square - especially the ground floor. The salesmen there have years of experience of picking out people new to Singapore. They notice what you are carrying, and they adjust their sales pitch accordingly. You can find bargains there but be careful because it can be like entering a lion's den for the uninitiated.
Always research your prices first and don't be swayed by the salesman to buy something else for which you don't know the price. Be careful of 'extras' they offer to throw in for free because you may not be getting the bargain the salesman says you are.
My brother lives in Singapore and he only ever uses Parisilk in Holland Village whenever he wants photo or electronic gear. He maintains their prices are low, and that they don't try to rip people off. He says that when he buys from them he doesn't need to do lots of research because he trusts them to give him a fair price.
I bought some gear from there recently and got good prices. It's not a place to go if you need a lot of advice. They are really only interested in turning over stock quickly, so go there if you know exactly what you want and exactly how much it should cost. It's always busy.
http://phil.uk.net/photography/gitzo_gt2541ex_tripod.html