Anyone looking for a roommate for their tech startup? I'm a single person founder.
You can probably get quite a bit of general research done before you head out and save yourself a lot of time.
The first thing you need to do is pop up google earth and take a look at the san francisco bay area to see that "silicon valley" can cover a lot of territory. You will probably want to have a general idea of what region of the valley you want to be located in; if you are just coming out to be a founder of a ramen-startup then you have a lot of flexibility, but you might also want to consider the fact that you might eventually need/want to get a "day job" or have others join your effort (which means that you might want to consider various commuting distances for places you are considering.)
If you have no other plan beyond "go out to silicon valley and change the world" then I would probably suggest that you stay out of San Francisco (too many fun social distractions) and aim for that suburban strip from San Mateo to Sunnyvale. This area is generally close enough to CalTrain that you can get in and out of SF with just a bike and you are more likely to replace social evenings at a club in SF with an entrepreneur meet-up in Palo Alto. Eventually you will need/want a car for general transit, but this particular zone will make it possible for you to get by without one for a while if necessary. After a year of this you will know the area a lot better, have a better idea where you want to live next, and will hopefully have made a bit of progress on your startup.
Start looking for a place on craigslist. You might find something you like, and at the very least it will give you an idea of what you will be looking at for rent in various locations.