Sometimes even the simplest things can bring a big boost in usability. A small sampler I came across recently:
letsfreckle.com: clear text password field – which you can of course turn into a regular one by checking a checkbox in case someone is standing behind your back with the intention of stealing your future freckle password (only God knows what could happen then)! Beware of the (web 2.0) ninjas though, they can hide pretty well – so be sure to turn on the password hiding if you are sitting in a black room!
omgbloglol.com: If you comment on an article, you can check a checkbox stating that you’d like to receive an e-mail if anyone makes a new comment. I’d like to have this everywhere (yeah I know about services like www.cocomment.com and co.mments.com but I found them clumsy compared to the above solution)
news.ycombinator.com: Simplest. Signup Form. Ever.
It would be great if other sites would realize that you don’t necessarily need your mom’s maiden name and similar info to sign up – it’s perfectly ok to supply that later on.