Here are some great resources:

• a nice, gentle tutorial — Learn Smalltalk with Prof Stef
• the most actively developed Smalltalk — Welcome to Pharo!
• a free book — Updated Pharo by Example
• a MOOC (massive open online course) — Live Object Programming in Pharo
• some great videos — Smalltalk 4 You
• a book that I like (not based on Pharo) — Smalltalk by Example
• another book that I like (not based on Pharo) — Computer Programming using GNU Smalltalk
• some additional resources — Resources

This book (not free) is my favourite for learning how to use Smalltalk for object-oriented programming: Smalltalk, Objects, and Design, by Chamond Liu.

I myself have published a whole bunch of Smalltalk tutorials. The latest ones are:

• Learn How To Program
• Teapot: Web Programming Made Easy
• How to use the Pharo Debugger

IMPORTANT UPDATE: There is a new Pharo MOOC that starts on October 16th, 2017. Sign up now!