Just 6km from Can Tho in the direction of Soc Trang is Cai Rang, the biggest floating market in the Mekong Delta. There is a bridge here that serves as a great vantage point for photography. The market is best around 6am to 7am, and it's well worth getting here early to beat boatloads of tourists. This is a wholesale market, so look at what's tied to the long pole above the boat to figure out what they're selling to smaller traders.
Cai Rang can be seen from the road, but getting here is far more interesting by boat (US$10 to US$15). From the market area in Can Tho it takes about 45 minutes by river, or you can drive to the Cau Dau Sau boat landing (by the Dau Sau Bridge), from where it takes only about 10 minutes to reach the market.