Please supply a list of online travel agents that would allow me to
book an inexpensive weekend roundtrip flight from Shanghai to Hong
Kong.

I see that I'm able to use Travelocity.com, but I'd like to know if
there are other sites that I would be able to use. The website doesn't
have to be in the U.S., but it would be helpful if it were in English.

http://www.cheaptickets.com

Daer SAMBOSTON
I used the following sites to get fares for Shanghai to Hong Kong Departing 
April 22 (Friday) and Returning (Sunday) April 24

www.travelocity.com   $417.00
WWW.cheaptickets.com  $418.00
www.onetravel.com     $422.00

All fares above fly with Eastern China Airlines
You can also try mobissimo.com which list fares with onetravel using both 
Eatern China Airlines and Dragonair Hong Kong. Fares with Dragonair are 
listed at $500. You may also wish to call these airlines directly to
see if they will give you a better deal than the Travel Agencies.
Mongolia

http://www.wacts.com/index.asp

Where are you at?  If you book at any China Eastern office in SH you
can get a good deal.  I use the one on Taixing Road.

If you're booking less than a week in advance, it may make sense to
fly to Zhuhai and take the ferry across to Hong Kong.

u can get ticket through www.ctrip.com,the largest online travel
company in China which was public owned in NASDAQ sotck market,they
accept credit card and can provide E-ticket/you can check in at Pudong
airport directly.the website www.ctrip.com provide  English service.