The SparkFun logic level converter is a small device that safely steps down 5V signals to 3.3V and steps up 3.3V to 5V. This level converter also works with 2.8V and 1.8V devices.
The DS75176 is equivalent to the SN75176
Begone, hard-to-program USB devices! At the hands of my FT232RL chip, you will behave like a serial comm port!
he ST232 is a 2 driver, 2 receiver device following EIA/TIA-232 and V.28 communication standard.
The DTE RS-232 module is a tight and tidy way to convert RS-232 (computer-level) signals down to a microcontroller level signal strengths. DCE means it's configured as a "Data Communications Equipment" (with 9 holes).
Because the Arduino (and Basic Stamp) are 5V devices, and most modern sensors, displays, flash cards and modes are 3.3V-only, many makers find that they need to perform level shifting/conversion to protect the 3.3V device from 5V.