It can be difficult. I'm just speaking for myself but I usually like to choose my own apparel (maybe a gift card?). I'm in agreement with what
@SkipdiverJohn said about personal form and fit -and add in style as well.
Anyway, my usual online purchases have been made from the following:
Nashbar.com -sometimes bargains can be found, and they usually have some form of coupons at some point. But they can also sell some stuff that isn't the best quality. Having said that, I'm still wearing Nashbar own brand mtb shoes and shorts after 20 years....
Performancebike.com -they are owned by the same company that owns nashbar, so very similar. I tend to think of Performancebike as being just a bit more upmarket.
jensonusa.com -solid web site, have been going for quite a time. Sometimes you can get a bargain, but usually more expensive.
coloradocyclist.com -similar to Jensonusa.
amazon.com -yes, they have almost everything an online bike store would have, and at competitive prices (and usually the items are sold from the online bike stores instead of amazon anyway). I've used them but always try to use someone else if I can as they aren't great to their workers IMHO.
Where in the north east are you? I know myself and RockyRoller are in Mass.