As Sullivan points out, many of the far-right talkers are enjoying a bump in the ratings. There are many discussions and debates to be had about this, but there's a broader point here.
In 2001-2005, when a conservative Republican president was riding high, cable news and the establishment media silenced opposition voices (just ask Maher, Moore and Donahue). But now that a liberal Democratic president is doing gangbusters, cable news and the establishment media appears to be encouraging opposition voices.
Weird how that works. Opposing popular Republican president on TV = bad. Opposing popular Democratic president on TV = awesome. Damn you, liberal media!
Adding... I should note, too, that ratings success has something to do with ideology, yes, but more importantly, the host or talker has to be good (or, in the case of Glenn Beck, shocking) at what they do.