If you're in L.A., the annual L.A. Times Festival of Books will take place at UCLA campus on the weekend of April 25 and 16, 2009. It's a free, 2-day event (except for parking costs).
Generally a very fun event for book lovers and people watchers.
Ways to make it an economically-savvy trip in these times:
take public transportation to UCLA (or stay with a friend on the West Side of L.A. so the bus/train trip isn't so long);
pack enough snacks, drinks, and meals to avoid $20 hot dog meal deals -- there are plenty of campus locations to make your day a family picnic;
leave the ATM/credit card at home and budget the most cash you plan to spend on books -- very important for impulsive book addicts like me;
read the schedule of panels and writers to decide your schedule for the day(s) -- it can be like free writer school for the day;
or volunteer for the festival and get your parking for free, get a t-shirt, and one free meal for a few hours of service. I've volunteered before and it's not hard work -- keep a line of people in order, escort an author to a panel, collect evaluations at the end of a panel.