This one works on Blogger sites. I could live without their ad at the bottom, but they have a very clean style - it brings up another window and then allows you to simply close it with a button. Very well thought out and very fast. Worthy of note.
You have to have such as tool on your site in order to get more subscribers. You can also BCC that email to yourself, if you'd like to ask them separately to join your email list - but this might be asking for trouble. However, it would be interesting to see who is actually using the tool and what they are saying...
Tell A Friend Script: "Tell A Friend Script
This Tell A Friend Script was created to make it easy for fellow webmasters to add 'Tell A Friend About This Page' functionality to their web sites. This tool is provided 100% free-of-charge for unlimited use and is not supported by advertisements. There is a small blurb at the bottom of each email that reads 'powered by ITistic (www.ITistic.com) - Complete solutions for technology driven business'. Please tell your fellow webmasters and colleagues about this useful tool! "