I recommend Brand Factory. I like branded garments, but I only go for the ones who respect quality and maintain quality, like John Miller's for shirts, Arrow for trousers, Live-In for jeans. I don't usually buy for full retail price. I'm always looking for discounts and deals. Brand Factory is very satisfactory in this regard.
The Brand Factory outlet I've been to is on Hosur Road, in Wilson Garden Area (near Abhay Hospital), walkable from Wilson Garden 10th cross bus stop. Great selection of quality brands, and the place always has some offers or discounts going on. If you search around inside the place, you will find a good deal going on on some good brand, like buy 3 get 2 free, or if you're lucky, buy 3 get 4 free
There may be another Brand Factory somewhere else in Bangalore.
Some of the MegaMart outlets will also have some really good deals running. There's one on Gandhibazaar main road, and a pretty big MegaMart Mall right next to Deve Gowda Petrol Bunk. I haven't been there, I've heard it's really worth checking out.
Live-In has a factory outlet somewhere near Koramangala. I don't know the road's name, but it's the same road on which we find Krupanidhi College (close to Koramangala, the road connecting Madiwala Bus Stop junction to Inner Ring Road). They always have good deals, and the quality is great. It's quite a small outlet, we can't expect a huge selection there. I usually go there if I'm looking for something very specific, like jeans, corduroy or trousers.
If brands are not your thing, then as previously suggested, Chickpet is a good area to hunt for clothing and fabrics.