The sheer number of introdoctory books to statistics is overwhelming. You should use any text that appeals to you (language, style, more or less mathematical etc) and uses examples from your field(s) of interest. The references below have been chosen for their pedagogical qualities. Note that the basic tools of statistics have not changed much in recent years and "classical texts", still in print and still used, are often better written than more recent publications.

Please bear also in mind, that depending on your scientific field and the kind of data you are analyzing, specific statistical tools are more or less important.

• Veaux, Richard D. De, Paul F. Velleman, and David E. Bock. 2013. Intro Stats (4th Edition). Addison Wesley.
  A textbook written by gifted teachers of statistics; has many examples, as well as a CD that includes Activstats (a highly acclaimed e-learning software developed by Paul Velleman).
• Wonnacott, T. H.; Wonnacott. 1990. Introductory Statistics. 5th edition. Wiley: NY.
  A classic. Still widely used, accessible textbook; translated into many languages
• Marsh, Jane & Elliott-Catherine. 2009. Exploring Data: An Introduction to Data Analysis for Social Scientists. Polity.
  An introductory text, written for social scientists; the expanded 2nd edition has many examples with SPSS.
• Erickson, Bonnie, and Terry Nosanchuk. 1992. Understanding Data. 2nd ed. Taylor & Francis Group.
  An introduction for social scientists, stresses both exploratory and more confirmatory approaches.
• Gonick, Larry, and Woollcott Smith. 1994. Cartoon Guide to Statistics. 1st ed. Collins.
  Very sucessful to get across the most important concepts of statistics.
• Klein, Grady, and Alan Dabney. The Cartoon Introduction to Statistics, 2013.
  Another well made cartoon introduction
• Blalock, H. M. , Jr. 2006. Social Statistics. Revised. Mcgraw Hill Book Co.
  A classic text (first edition 1960)