Very good recommendations from firefox. Check out these bags and stick to the right gear.
The 200 has more than enough space if your dslr is normal size, prime lens or wide lens. A bit tight or even small for pro type of dlsr, 3 large lens and a large flash. Do try it out physically before buying.
Lowepro Nova 4 AW. $60 from cathay IIRC. Quite small on the outside but can stash a surprising amount of gear. Only downside is it looks abit . Depending on the lenses you have and whether ur DSLR has a vert grip, you can put the body + 3-4 lenses + flash + some other accessories (batts, filters, etc)
Don't forget to get the backpack strap as well if you are going for the Domke F2, with it you've got a sling bag that you can also carry on your back. You can forget about the post office-style shoulder pad though, S'pore's humid weather does nasty things to it and it really starts to smell funky after a couple of years.