According to my receipt, I ordered a package of 2 IR detectors from Hobby Engineering -- SFH205f IR Photodiode – Hobby Engineering -- but what I have on my desk has 3 wires instead of the two shown here. Maybe the official ones are somewhere on my desk, but all other parts of similar shapes are accorded for.
How do I connect a 2 or 3 wire photo transistor to my Arduino? Right now it's just 5V -> IR -> Analog In. The 3 wire I've tried as 5V to pin 1, Analog in Pin 2, Gnd Pin 3. Anything different?
The transistor will pass current proportional to the light falling on it. You'll need to check the datasheet, typically ~0-4ma. Connect the emitter to 5v through a 1250 ohm (1k2) resistor, and the collector to ground. Connect the emitter-resistor junction to the analog input, then analogread away! You won't get rail to rail, but probably close.
As far as the 3-wire device you have is concerned, one of the wires is most likely a "base" wire; IR detectors are generally phototransistors - some are two wire (with the base being driven only by the IR light falling on it), while others are three wire. The third wire connects to the base of the phototransistor; you can add a bias resistor and apply voltage (and/or set up a voltage divider with a potentiometer to vary it) to change the level of IR light needed to turn "on" the transistor (essentially making it more "sensitive" - it also might increase noise and reduce accuracy if you are looking to sense levels instead of just on/off).
Check the actual datasheet for the part if you can find one; it should say what exactly all the leads are, what they connect to, and other specs for the devices.
There are also 3 terminal IR receiver ICs that include the 38hhz filtering and auto gain circuitry. They are used in nearly all consumer remote controls. Here is a typical one: