Chroime, Opera, Firefox and OpenOffice all have open source Latvian spellcheck.
What about Google Docs?
As in the "new" Google Docs right-click menu of browsers has been disabled - and it was the way how I implemented spellcheck function in Google Docs at that time, I have happily moved to Microsoft WebApps for the purpose of creating text documents: spellcheck works very well, and , in general, after recent overhaul WebApps is much more pleasant experience for creating text documents than Google Docs.
Without spellcheck, Documents of Google Docs are of Word Pad functionality for me- then it is better to use the WordPad- it is faster and smoother.
So, I just occasionally coming to Google Docs to check, may be this basic, kindergarten level problem with spellchekcing in "new" Google Docs has been resolved, but the time being, since May 2010 until now,the problem is here.