What sort of resolution are you looking for? sub nm?5 nm?etc
Typical lab grade laser measurement tools typically use "newton's rings" as an interference pattern to read their laser frequencies. This method is only limited by the accuracy of your measurement of the curvature of the lens and the measurement of the pattern radius.
http://en.wikipedia.org/wiki/Newton's_rings
Downside: you will most likely need a laser whos frequency you know
Upside: your limiting factor is then determined by how accurate you know the frequency of your calibration laser.
Downside: multimode lasers can produce slightly confusing interference patterns if you don't know what you are looking at
Note: if you do this method measure the furtherest visible ring as it will give you the least uncertainty in your calculation.
Diffraction methods: As stated by an above poster you can actually use a diffraction grating to do this as well. The upside to this is you don't need a calibration laser but you will need to accurately know the dimensions of your grating.
http://en.wikipedia.org/wiki/Diffraction_grating
Here you have: d*sin(angle)=m*wavelength where d is the spacing of the gratings slits, m is the mode number from the incident beam (indicents beam number is 0 and is just the geometrical reflection or straight path through your grating) and the angle is the angle between the mth mode and the 0th order mode.
To do this you can use a CD or DVD or order a diffraction gratingthatiscalibratedfor really cheep. DVD's actually have very high accuracy on their spacing so they make good subjects (note ideally the spacing for the grating should be <the laser wavelength, you wont see diffraction of a red laser off a CD for example).
You then place the grating at a set location aiming the reflection at a wall. You now need to measure the distance from the grating to the wall and the distance between the modes and via some quick geometry/trig you have the angle and thus the wavelength of your laser.
