There are two basic types of flash memory: Single-level cell (SLC) and multi-level cell (MLC). By using multiple voltage levels to store information, MLC memory can pack more data into the same area of silicon, bringing price down. However, this improved density causes disadvantages when it comes to read/write speeds and write endurance. Therefore, lower-cost cards typically are MLC types, while higher-cost cards are SLC.
You should also be aware of the rather complex supply chain for these cards. In the flash fabrication department, Toshiba partners with SanDisk, Intel partners with Micron, and Infineon, Micron, Renesas, Samsung, and ST Microelectronics round out the major suppliers. Most of these companies also make the controllers for the memory, but there are even more companies that make their own controllers. See this 10-k filing by Lexar from way back in 2005:
[Excerpt 1] We compete with semiconductor companies that manufacture and sell flash memory chips or flash memory cards. These include Hynix, Infineon, Micron, Renesas, Samsung, SanDisk, ST Micro and Toshiba. Micron and Intel have recently formed a joint venture known as Intel Micron Flash Technologies. SanDisk and Toshiba jointly develop and manufacture both low-cost and high-performance flash memory through their Flash Vision joint venture.
[Excerpt 2] We also face significant competition from manufacturers or card assemblers and resellers that either resell flash cards purchased from others or assemble cards from controllers and flash memory chips purchased from companies such as Renesas, Samsung or Toshiba, into flash cards. These companies include Crucial, Dane-Elec, Delkin Devices, Feiya, Fuji, Hagiwara, Hama, Hewlett Packard, Data I/O, Infineon, Kingston, Kodak, M-Systems, Matsushita, Memorex, Memory Plus, Micron, PNY, PQI, Pretec, Ritek, Samsung, SanDisk, Silicon Storage Technology, SimpleTech, SMART Modular Technologies, Sony, TDK, Transcend, Viking InterWorks and many others.
[Excerpt 3] In addition, an increasing number of companies are manufacturing their own controllers, including Genesys, Hyperstone, Prolific, SanDisk, Sigmatel, Silicon Storage Technology, SMI, Solid State System, Sony and Zoran. Such companies either combine their controllers with flash memory from third parties to manufacture their own flash cards or sell their controllers to third parties who use them to assemble flash cards. Additionally, major semiconductor companies such as Infineon, Micron, Renesas, Samsung and Toshiba have also developed or are currently developing their own controllers that will likely compete with our controller and/or card sales.
Importantly, note that some manufacturers, including the Kingston brand praised in other answers to this question, doesn't manufacture any flash memory. They buy it from their competitors. The only value-add that Kingston offers is branding, packaging, testing, and controller firmware.
That said, I don't know which of those three links use which type of memory, or which Flash foundry, or which controller. I know that the SD card manufacturing industry is full of counterfeits, so be careful who you buy from (See this post from Bunnie Studios for an example of the counterfeiting in Kingston cards).