You should try to ask somebody out in person, but if not, a quick phone call should do the trick. Never by email, it leaves too many opportunities to flake without having to confront you, you know:
"I got your email too later."
"I accidentally delete it."
"my brother deleted it."
etc. etc. etc.
Women are fascinated by the whole E-mail experience though. Just like they loved getting letters, I guess email is the thing. You can use this to your advantage when first making contact with them, right after you meet them. They love giving out email, its very very weird. A quick short email is enough to get her happy, but don't use it to set dates, unless its somebody you've been seeing for a while, and who doesn't flake, in other words, who you know won't use it against you. But why take a chance, just dont' do it.