Recommended college ecology texts
Begon, Harper and Townsend. 1996. Ecology: Individuals, Populations and Communities, 3rd ed. ISBN: 0632038012.
Begon, Townsend and Harper. 2005. Ecology, 4th ed. ISBN: 1405111178. (This book has just been published. I've not seen it yet, but it is the next edition of the first text so it should be good.)
Molles. 2002. Ecology: Concepts and Applications, 2nd ed. ISBN: 0072493526.
Gotelli. 2001. A Primer of Ecology. ISBN: 0878932739.
The Begon et al. text is the one used in rigorous undergraduate ecology courses. It presents the material in the most comprehensive and up-to-date way of the various texts. The Molles text is less rigorous, but more accessible to non-majors. It may be particularly useful for teaching high school students. Gotelli's book, as the name indicates, is not as complete as the Begon et al. text, but it is well written and fairly thorough on the topics it covers.