The conventional answer to this has always been that you can do anything with an English degree, and a recent MLA report bears that out: people follow a wide range of careers after getting their English degree. That said, some careers are more common than others. Here's the table reproduced from the report of a survey of English degree grads from 1990-1999.
What you can see here is that 21.4% of grads are in Education at some level (this includes teaching in non-educational institutions). I think it is reasonable to say that those grads are probably making direct use of their English degree. The next largest category is artists, editors et al (14.4%). There's a good argument for saying English is as good a preparation for such careers as any major (particularly if the English degree includes professional writing curriculum). But after that it gets a little sketchy. That's not to say that English wouldn't help you; it's just hard to say that English would be more appropriate than History or Philosophy or Comm Studies or Psychology or Economics or whatever.
In short, more than 60% of English grads end up in professions that are only tangentially related to their undergrad study. The report also notes that 46.4% received graduate degrees. It might be interesting to see how the career distributions of those with grad degress as opposed to those without, but that information isn't in the report.
I am not one to say that English degrees ought to be constructed primarily around job preparation. In fact, I think prepration for a specific career is generally not a good strategy for an undergrad major, with some exceptions (e.g. those that require certification–public school teacher, nurse, etc.). So I'm somewhat curious to know what others think of this data. What, if anything, should it tell us about our degree programs?