I've used Paul Kutsche's Field Ethnography: A Manual for Doing Cultural Anthropology (Prentice-Hall 1998) with intro-level undergraduates to good effect. The book is small and accessible, and provides guidance for students to conduct a series of increasingly-developed local mini-ethnography projects. There's really no limit to cultural behaviors for them to document and interpret. Some interesting topics I've seen have included things like patterns of library study-table choice based on location and gender of existing studiers, greetings or absence of greetings among walkers/bikers/skaters on a multi-use exercise path, documenting language diversity at a local recreation area. It's a great way to get students thinking about the cultural construction behind everything they do!