I live in Portland and commute 10 miles each way all year 'round day and night. To be honest, it really doesn't rain all that much up here in the summer. You might get a day or so each week........ Winter is a whole diffferent story, though this winter has been pretty dry. Technically speaking, we are in a Mediterranean climate, which is defined by being wetter in the winter than in the summer.
Having said that, I have tried almost every piece of raingear out there. Believe it or not, the best thing I have found is the Propore cycling jacket, that runs about 32 or 34 dollars at REI. These things work about 10 times better than ANY Goretex or Precip jacket in terms of both breathability and waterproofness. OK, they are not so durable, but hey, I could buy 6 of them for the price of one Goretex jacket. Each one lasts me about a year and a half. Even on cool sunny days, they keep me much drier than my Pearl Izumi silmond windbreaker, whch is supposedly breathable.... And they weigh about 5 ounces. This is a great way to go, especially if you are a visitor who will not be riding in the rain much after leaving here. I can't say enough good things about them.
The neoprene booties, as mentioned, are a terrific thing in the winter. I use the fleece lined Performance brand ones, currently on sale for 20 bucks in my local Performance store. In the winter, my feet are the warmest part on my whole body and they used to be like ice cubes in any ride over 20 minutes. They might be overkill in summer....... Sealskinz socks over light liner socks work fine also and are lighter, though not as warm.
Any kind of Goretex liner ski glove works just fine for me.
Wear a helmet that has a visor! This goes a long way to keep the rain out of your eyes.
OK, the other thing you need in the wet is wool. Specifically, merino wool, like the Smartwool, Ibex or some of the stuff Rivendell carries. I have about 15 Patagonia Capilene long sleeved tops that now sit in the drawer since discovering how much better wool is when it gets damp. The socks are terrific and also the zip turtleneck. Merino wool does not itch........ try it ..... you won't go back to anything else....
As mentioned full fenders are pretty much essential......
Go to great lengths to keep your sleeping gear dry. Lining conventional panniers with plastic works just fine...... no need to invest in Ortliebs or Vaudes ..... though they are nice, indeed.
Lastly and maybe most important..... adjust you attitude! Keeping a sunny outlook is imperative. Hey, it's just water and if you are wet but warm, what's the big deal? You can get chilled if you stop though, so either have warm spare clothes or a warm place to duck into. You will find LOTS more coffee shops up here and for good reason! The sun WILL eventually come out and you can dry out your stuff so don't worry...... just have fun!