Personally I think it's pointless buying a chain online unless you have a chain breaker.... (or grinder and pinpunch).... because you'll have to trundle off to a bike shop to get it shortened, and if you haven't purchased it from them they are likely to charge you... it will end up costing more in the long run..
If your old chain was an ok length before it stretched, just take that to your nearest bikeshop and ask for a DID (or your prefered brand/quality) with the same number of links... They should break/shorten it for free... and if you end up needing to remove a couple more links at a later date they'll proberly do it for free also...