Okay, so I am going to build a small weather station out on my deck. Going to measure barometric pressure, relative humidity, temperature, wind speed, and hopefully, rainfall. Now I can get chips to measure most of those things. Was thinking about using a one of those spinney things with the little cups (with little neodymium magnets and a hall effect sensor) for the wind speed. But for the life of me, I cannot seem to be able to wrap my head around an easy way to measure rainfall. Any ideas?
I've been thinking about order the TX32U-IT rainfall sensor by LaCrosse. It is less than $10 from Amazon and is designed to work with their 915 MHz base stations. It appears to be of the tipping cup style so it will have a magnet and probably a reed switch that I would replace with a Hall sensor. You could probably remove the transmitter to use in another project. At that price, I'm willing to take a chance on one.
Otherwise, I have in the past used and still own the tipping cup sensor that you could order with the Dallas Semi weather station. I'm not sure if you can still buy those anywhere but a company called AAG still makes the wind speed/direction sensor and I have one of those as well. It is $79 and has an RS485 interface. ASG may have the rain gauge but their website is hiding it pretty well if they do and they don't respond to email very quickly. They will ship you a wind speed/direction sensor though, if you are patient. It took about 2 weeks to get mine.
Wow, the TX32U-IT is definitely worth a gamble. I was considering a beaker and a scale! lol. As for the wind measurement, I am trying to build this as cheaply as possible and also build as most of it myself as I can. I was thinking of cutting 2 ping-pong balls in half to use as the cups. I am off to wallyworld for the TX32U-IT now tho. 
I'm anxious to hear what you find inside. I think the most important part of the anemometer is probably the bearing assembly. as long as that is as frictionless as you can get it you should be okay.
Bah! None in stock. They ordered it for me tho. Maybe Monday...