Best way to store case-insensitive data?

I have a column called "email" that users login with, thus I need to
be able to lookup email very quickly. The problem is, emails are
case-insensitive. I want foo(at)bar(dot)com to be able to login with
FOO(at)Bar(dot)com as well. There's two ways of doing this, that I can see:

1) Every time I lookup an email in the database, do a case-insensitive
ilike, or cast both sides with LOWER(). I think both are slow,
correct?
2) Every time the user updates or saves their email, store it in
lowercase, and every time I lookup an email, pass in a lowercase
email. This is somewhat of a bug farm because one might miss some
little spot in a piece of code where an email is compared or updated.

Is there any way to tell postgres to always store data in lowercase
form, or just have a flat out case-insensitive column? Thanks!

Mike