Longshang Vegetable Wholesale Market

155 Beidi Road
North side of the Hongqiao Airport.
上海龙上农副产品批发市场
北翟路155号
Everything vegetable you buy at the wet market in Puxi probably comes from here.

Caojiadu Wholesale Flower Market 

1148 Changshou Road
On the north east corner of Wanhangdu Road and Changshou Road
曹家渡花市
长寿路1148号
Take note, there is a flower and bird market in the front. To access the wholesale market, head to the building in the back.
One of the big suppliers of tulips told me that although this market is relatively small, it sells more flowers than any other market in Shanghai. Buy flowers by the bundle for cheaper than you can buy a few alone. The wholesale market closes early, around 4pm.

Jinsheng International Home Deco and Hotel Supply Market

185 Tongchuan Road
Near Langao Station of line 7
金盛国際家居辦公楼
铜川路185号
North east, central part: Housing supply, more along the lines of designer and branded lines, not exactly wholesale; doors, flooring, bathroom, beds, windows, kitchens, building supply etc.
Back and western part: hotel supply; equipment, supplies, dishes, uniforms, etc.
*Note, a separate building in the south west corner is also hotel supply.

Stationary and Business Supply Wholesale Market 

1108 Zhongshan North Road
South West corner of Zhongshan North Road and Hutai Rd. Main entrance on Hutai Rd.
上工批星沪中文化礼品市场
中山北路1108号
Paper products, pens, envelopes, business equipment, etc.

Shanghai International Packaging and Printing City

1111 Zhennan Road, Putuo
上海国际包装-印刷城
真南路1111号
A market devoted to printing and packaging of all sorts.

Imported Wholesale Foods

1255 Lianhua Rd, Minghang District
闵行区莲花路1255号
Mix of Imported and local foods including; dairy products (butter, cheese, etc), baking ingredients, all nuts, spices, condiments, flours, canned goods, sugars, chocolates, etc. This is the place to go. The imported American, European, Indian, and other goods mainly on the south end of the market.

HEC – Hotel & Restaurant Supply

345 Aomen Lu, Putuo District
酒总酒店设备大卖场
普陀区澳门路345号
http://group.heconline.com.cn/
Hotel & restaurant supplies. Popular and well known in the expat community for its selection and clean and professional shopping environment. Take note of the other wholesale shops off the street directly to the east of this place.

Caoyang Wholesale Fruit Market

1366 Caoyang Rd, Putuo District
上海山华果品市场北区
普陀区曹杨路1366
Largest (its HUGE) wholesale fruit market in Puxi, both Chinese and Imported fruits

Tongchuan Marine Market

800 Tongchuan Rd, Putuo District
铜川水产市场北区
普陀区铜川路800号
Anything that lives in the water (watch out for the eel aisle). There is a small hotel supply and dry goods market on the west side and set back in on the north end.

Huanghai Frozen Foods Market

38 Beishi Rd, Putuo District
皇海冷冻食品商行
普陀区北石路38号
Imported and Chinese meats: beef, pork, poultry (turkeys), fish, etc.

Jiuxing Comprehensive Market

闵行区九星综合市场Minhang District
Southeast block of Caobao Lu and Hongshen Lu, Minhang District
http://www.jiuxing.com.cn/
Building materials, hardware, kitchen, bed & bath, furniture, hotel & restaurant supplies, fire & security, office supplies, signs, other. This place is huge and has its own internal road names with traffic lights and everything. You can find just about anything related to the above categories. Everything here is wholesale.

New Century Automobile Parts City 

416 Changhe Rd (the block north west of Zhennan Rd and Changhe Rd)
普陀区常和路416号
Mainly has parts, supplies, and accessories for all types of bikes (bicycle, electric, motor). Go here to find neon lights for your electric bike, a soft seat, or that pink matte finish on your Vespa scooter.

HONORABLE MENTION

Baoshan Audio & Video City (Electronics) (reconfirmed Nov, 2014)
111 Baoshan Rd
上海音像城(宝山路)
闸北区宝山路111号
Not a true wholesale market, but they specializes in second hand electronic goods and repairs
Mobile phones, computers, cameras, printers, stereo equipment (KTV), you can even buy a taser.

source:www.shanghaiexpat.com