I would look into the URAP - Undergraduate Research Apprentice Program. I worked with an English prrofessor for two semesters on a folklore project through this program and LOVED IT. They sohuld have a list of the positions available at the beginning of each semester.

research.berkeley.edu/urap/

Are you looking for paid or unpaid? if unpaid, you can just start looking through the professor's bios/CVs/lab websites and contact the ones who are doing research you are interested in. Most are happy to have more free labor and don't bother to post when they are looking for unpaid undergrads so don't be shy. Start emailing professors who you want to work with (but don't be surprised if some of them don't get back to you).

Paid positions are a lot harder to find, so URAP is a good alternative since you get class credit.