Let me amend that. Top five things to see in Akihabara that do not involve a Maid Cafe. Because, come on, these costumed girls are all over Akiba handing out coupons. You don't need my help to find one. Akihabara is much more mainstream than the you-will-never-touch-my-virginity Otaku enclave you might imagine.
Haha they are all over, I agree. I remember seeing large groups of them all over the streets.