How does one perform a case-insenstive query on test or char fields

Hello,

Well, the subject line pretty much says it all. If any clarification
is needed, what I want to do is as follows:

SELECT * FROM table WHERE thisfield = 'some text';

How would I rewrite this query to search through the table looking at
the text in the column "thisfield" for the string "some text" but have
it perform a case insensitive search?

Thanks,
Andy