Is there a good field methods book that covers terrestrial ecology?
Take a look at Field and Laboratory Methods for General Ecology by James E. Brower, Jerrold H. Zar, and Carl N. von Ende.

If you are only interested in plant sampling techniques, an great resource published by U.S. Bureau of Land Management is Measuring &amp; Monitoring Plant Populations by Caryl L. Elzinga, Daniel W. Salzer, and John W. Willoughby.

Another great resource that covers wildlife research and management techniques (2 volume set) is The Wildlife Techniques Manual published by The Wildlife Society and edited by Nova J. Silvy.