Memory card readers aren't really something special but one of X-bit Labs' reviewers went through the trouble of reviewing 27 of these devices!
Every model covered in this review, both internal and external, is connected via the USB interface, so the difference between them is in the design of the case, the connector at the end of the cord, and in the controller chip. I can tell you right away that each model comes with the same accessories that include a USB cord and a disc with drivers for old OSes (card-readers don’t require special drivers from Windows 2000).
As for the controller, you don’t even have to take the device apart to find what model it is: every controller has a specific code, two four-character strings. The Vid string denotes the manufacturing firm, and the Pid string denotes the model number. These strings can be read with special programs, but I prefer the way that doesn’t require additional tools.
Check it out at X-bit Labs. One of the fastest memory card readers is the SanDisk Extreme, if you have 200x or faster memory cards this reader is recommended.