I have just finnished designing a laser for medical purposes and if you don't have to control the intensity of the laser you'll be ok. You will how ever not get away with just a resistor for very long. Lasers generate a lot of heat and need to be put in a suitable heat sink. As the temperature rises so does the threshold current which means the laser has to be driven on harder (never exceed the maximum current on the report card. Your laser will turn in to a very poor LED in a matter of milli seconds). The only way you will achive that is by designing a feedback circuit. Most laser diodes have a photo transistor built into the package. This is what you use to control the feedback. Be carefull if you use any laser diode in the visible spectrum. They are very static sensitive, more so that the invisiable ones. The other reason you need a feedback circuit is no two lasers operate the same. When you buy them you will get a report card with the threshold current, maximum operating current, monitor current (this is the current from the photo transistor when the laser is at full power) and the operating voltage over the laser diode. Each laser will have a number and that number is the number on the report card that has it's information. You will find that some at full power are just over the threshold current of others. There is no thumb rule you can use.
I also needed a detector because for medical you must have a seperate power detector (besides for the photo transistor inside). I used the OPT101 from Burr-Brown. It is a photo-diode with a built-in transimpedance amplifier and it had a pretty good frequency spectrum, peaking at about 850nm wavelength.
http://www-s.ti.com/sc/ds/opt101.pdf