I. Various Languages

BBC Languages
Language lessons provided by BBC.

About.com
This popular web guide offers also a collection of free online courses for studying different languages.

Hello-World
Lessons, activities, games and songs for studying English, Spanish, French, German, Italian, Chinese, Russian, and Indonesian.

Jim Becker’s (at the University of Northern Iowa) collection of resources for studying a variety of languages

Livemocha
A social networking site for lesson exchange between native speakers.
 

II. Specific Languages

Spanish

SpanishPod
Podcasts for learning Spanish.

123TeachMe.com
Free online Spanish courses.

ABCTeach
This collection of printables and worksheets contains also a directory for learning Spanish.

Chinese

ChinesePod
Podcasts for learning Chinese.

Chinese-tools.com
Lessons and tools for learning Chinese.

French

The French Tutorial
Lessons covering pronunciation, grammar, vocabulary and everyday French.

Francais Interactif
A comprehensive online French course from the University of Texas at Austin.

German

Deutsche Welle’s German language courses
With lessons for different levels and purposes.

Russian

Way to Russia
A Russian language online tutorial and a Russian phrasebook.