Linguists might always check the language departments on campus, e.g., English, French, German, Asian Languages, Slavic, Classics, Spanish, and our own SLP (Special Languages Program, listed at the end of Linguistics), but also check other departments for courses that are (sometimes) related to Linguistics, e.g., Education, Psychology, Philosophy, Anthropology, and Computer Science. If a Linguistics class is cross-listed with another department, check the course offerings in that department. You might find other courses there that pique your interest.
If you find a course title that titillates, but it's an undergraduate course, don't hesitate to check it out. Most undergraduate courses are also open to graduate students, and you can get graduate credit for those numbered 100 and above.
In any case, if you find a course you are interested in, but you're not interested in taking it for full credit, be sure to inquire about auditing the class or arranging to take the class for fewer units. Feel free to negotiate a plan that suits your interests and time. Most professors can be pretty flexible.
Being linguistics students, we'd all like to take language courses. Unfortunately, though, this is easier said than done. Nearly all language courses have classes five days a week at the same time. This means it is very hard to combine them with other classes you wish to take (especially since classes in linguistics often meet for longer than one hour). Either you have to lose a lot of sleep and do the 9 a.m. session, or take no other classes in one of the morning or afternoon. Many people thus resign themselves to the idea that third year is a good time to take language classes. Some people actually make good on this idea, while for others, it remains just that, an idea.
The linguistics department participates in an interdisciplinary program in Cognitive Science, and if you are interested in allied fields, especially Psychology, Philosophy, and Computer Science, you may have read about how you can get a Cognitive Science designation on your degree. But many members of the faculty seem totally apathetic about this program. Some people feel that it may be better to just take the courses you are interested in and show evidence of your broad interests in your research and conference presentations. On the other hand, a Cognitive Science designation can hardly hurt, if you have any inclination toward getting a job later on doing such interdisciplinary work. See http://www-linguistics.stanford.edu/~kyle/program.html#cog for a list of the courses that are currently approved for the program.
Finally, it is possible to take courses for credit at UC Berkeley, although students rarely avail themselves of this opportunity because of the difficulty of the commute and the fact that UCB is on a totally different schedule than Stanford. Check with the Stanford Registrar to get a form for transferring credit hours.