Smalltalk is programming language (and environment) created in Xerox PARC during 1970s and 1980s. Also its usage peaked during beginning of 90-ties it is still in use.
Below is collection of links i found useful to get overview about Smalltalk and its different dialect.
Main Dialects
VisualWorks
Descendant of the original Smalltalk-80 from the Xerox PARC. Cross platform (mainly) desktop smalltalk. Commercial but has non-commercial license available.
GemStone/S
OODB, server side (no own GUI, usually used in combination with other client smalltalk). Commercial but limited version available for free (it is called GLASS, price list is here).
Blogs:
Dale Hendrichs
James Foster
Other:
Community site, documentation, materials on YouTube
VA Smalltalk
successor of IBM VisualAge Smalltalk, commercial, cross platform
Dolphin Smalltalk
Commercial, tight integration with Windows (it is also Windows only).
Pharo
Open source (MIT license), fork of Squeak, cross platform.
Part of project is also very good free e-book Pharo By Example .
GNU Smalltalk
Open source (GPL license), focused on scripting and integration with Linux.
Other resources
Basic smalltalk tutorial.
Large collection of free books is here (.pdf)
Planet Smalltalk (Smalltalk RSS aggregator)
Seaside
Web Framework for Smalltalk, available in all main dialects.
Conferences
Smalltalk Solutions
ESUG (European Smalltalk User Group)
- Materials from 2009, 2008, 2007
- List of conferences