All of the above, but I find that too many ads from other companies on a quilt site turn me off. I appreciate timely updating of available fabric, online BOM clubs, competitively priced fabric and reasonable shipping. I know packing is costly, but when I see a notion that I must have, it isn't the price of the notion but get turned off by outrageous shipping. A handy hint area with screened contributions from customers would be unique.

I also like pictures of completed blocks or projects using patterns from books. Gasoline is getting costly, and a trip to the closest LQS costs me almost $6.

It's the kind of quilt blocks they show, and fabric selection

Ease of navigation, fast page-loading
Everything in the store organized logically, as in a real store.
Fabric sorted by manufacturer and line, other items sorted by type - pins all together, Thread Heaven and thimbles together, scissors and snippers together, etc.
Good selection, latest products - "New Products" category is helpful for frequent visitors
Ease of placing an order
Estimated shipping date and delivery date provided at time of order
Prices not out of line - if everyone else is selling a product for $22 and one site has it for $32, I tend to assume that all their stock is likewise overpriced and I leave the site.

When I visit a site...
 

I am looking for reasonable prices and shipping, quality, and I like freebies such as patterns, quilt labels or computer wallpaper featuring fabrics I like. I also like the sites with design boards so that I can see my choices against each other. When you are scrolling through lots of fabric, it's hard to keep them all straight and know what looks good together.

The first thing I look for is an easy to navigate site. If it is too slow loading or just a confusing site, I leave and go no further. If I can get around easily, I look for the type of fabrics that I like as far as style, colors, manufacture. Then I look at price. If all these things are good, I look at their shipping charge. If even that looks good, they have a new customer.
If it doesn't look good, I move on. There are just too many stores out there carrying the same exact fabrics. I am probably fussy but I believe that with my money I can pick and choose where I want to shop.

You have to be able to navigate the pages in an easy manner. that is very important to me. Then I look for all the other things everyone else has suggested. But if I can't navigate the pages easily....I go to another site.

i will shop online if the prices are good ,the shipping is reasonable , if it is something at cant get at my local quilt shop , and there website is secure and easy to checkout and see all there products

Price, selection, demos, ease of use to the site. Shipping vs. picking it up at a store.

I find the online shops most helpful when the LQS only has part of I line I want to use or has sold out a fabric that really is needed in the quilt. I prefer the sites that are easy to navigate and have a good search engine. I don't ever stay on a site that I can't use a search to find something specific.

I also shop online and at LQSs. But my LQS aren't that close. Two are 1/2 hour away, two more 1 hour, 2 more 1 1/2 hour. But one shop gives me 15% off for driving so far. Also, when I go to the LQS I always spend my money there. But I also spend my money online at FQS. I love that shop. (Fat Quarter Shop) Their presentation of their fabric is wonderful. I never want to open up the wrapped up fabric because it looks so beautiful. I also shop on ebay when I can't find a fabric and sometimes at thousands of bolts. I'll type in the fabric I'm looking for in my search engine and up will pop quite a few online places that I then go to to find what I need.