I think it is high time to create a thread meant solely for links to useful resources
Courses
Flash course for beginners
Another interactive course for beginners: Part I,Part II
And another
A1 level course in Russian
A2 level course in Russian (part 2 of the above)
A very simple course aimed at teens not from EU (has IPA pronunciation samples), complementary teacher's book with some exercises apparently there is exercise book as well, but it's nowhere to be found
A trilingual (the other two are English and Russian) course for kids
Another online course
High level audio course/detective story
There are some video courses found on this Youtube channel, but since they are intended for use on websites, they have no playlists. Note that they apparently are for kids living in Latvia. The sites are:
Based around Russian puppet show there are some more videos and audios, and a small dictionary on the site
A game show aimed at Russians (note that neither the hosts nor the participants are native speakers), this site also has some more material, but I've already linked other materials that appeared useful here (some of them are aimed more at the native speakers and there are two other video series -interviews for which you can download vocabulary used and videos about Latvian culture)
Tv series for grades 7 and up note that it is more like an advertisement for use of standard language also it is found on teacher's side of the site above, besides other videos (subtitled series for parents on language teaching and series for teaching about nature which has some vocabulary) and some exercises (linked below) it only has materials on such topics as teaching methods and designing lessons
Also this site ought to have downloadable books about and for minority education, but most links don't seem to work
Grammar & exercises
Exercises aimed at adults
...more of the same...
...and more it seems, unfortunately, that there are no answers
Listening exercises
more listening exercises
reading exercises
Word search puzzles
Exercise books for kids ages 6 to 9 and ages 10 to 12
Games/exercises for kids (these seem to be aimed at Latvian speakers, though)
Grammar tables
Grammar information in Russian
word analyzer
Another word analyzer
General information on grammar
Morphology exercises (you need to register so you can check your results later)
Orthography
Phonology
Correct pronunciation with exercises
Exercises for people learning Latvian as foreign language
Excersizes (some are for other languages)
Dictionaries
Picture dictionary (registering apparently gives you access to definitions and some other materials in Latvian)
Latvian-English
Letonika -From Latvian to English, Russian, German, Lithuanian, Latin and Estonian
http://www.tezaurs.lv/ - Various dictionaries, mostly Latvian to Latvian, except the following:
-Basic vocabulary to English and Russian
-Latvian to Russian with definitions
-Latvian to English idioms
-Latvian to Russian idioms
-Business terminology Latvian to English and Russian
-Latvian to Russian terminology
Diatrics
Translit converter
Keyboard layout software
Literature
Mostly classics
Fairy tales
More fairy tales
Mostly classics
Children's books (up to teens)
Music & video
National radio (1 News 2 Latvian music 3 Classics 4 Russian 5 Youth)
List of other online radio stations from Latvia
Latvian song lyrics
Online mp3 store
Another store with song previews
http://www.tvplay.lv/parraides TV content provided by MTG
http://ltv.lsm.lv/lv/raidijumi-a-z/ TV content provided by Latvian Television (note that you need to click on letters to get more choices and it also lists some shows you can't watch online)
Dialects & Sign language
General description of dialects (in Latvian, if you click links you'll get descritions of differences between dialects)
Latgalian Textbook Vasals
Latgalian ABC part I
Latgalian ABC part I
Teachers book for Latgalian ABC
Sign language dictionary
http://www.zimjuvaloda.lv Site about sign language in Latvian
The list was last updated in October 2013