Wright Research Center Profiles of over 20,000 companies from around the world, including 71 in Turkey. FinansInvest Nice profiles of Turkish companies, with charts and all kinds of company data. DBC Istanbul Quotes End of day quotes for Istanbul-traded stocks. Available in English, Turkish or Russian, this site has a lot of information about business in Turkey. Profiles of many companies, arranged by sector, are available.
Profiles appear to be written by the company themselves, so are more like sales brochures.
Although this might be a little dated, there's a lot of information here. You can search by company name or product, and you'll get address, telephone, fax, contact, turnover, exports and banks. There appears to be quite a few companies in this database. Turkish Foreign Trade Center Profiles of a very large number of exporters and importers. Organized by sector, this site gives name, address, phone and fax.