The main chain is JoAnn’s and Hancock’s, which I think most people find convenient and they do offer a fair amount of coupons so you can usually get a really good deal there. If you want high end, apparel fabric, I recommend Mood’s. I think they only have store fronts in NY and LA but they also have an online shop and if you sign up for their newsletters, you’ll get a notification when a fabric will go on sale. They can be expensive but they have really nice items. For online, I’ve purchased many times through fabric.com. They have a large selection, it usually arrives quickly, and I can usually find a promo code somewhere to use. I wouldn’t say they’re inexpensive but they offer a lot and I’ve never been disappointed. Also, they sell swatches so if you’re unsure, buy a swatch so you can see the fabric in person before purchasing more. Also, don’t forget to check out etsy, you might be able to find some unique fabric there. And if you’re artistic and want to design your own fabric, check out spoonflower.