I use the XPower Pocket Inverter 175 from Xantrex. There is no need for purchasing additional tips as you can plug in your regular laptop power cable. It also has a USB power outlet, and can be used in your car through the cigarette lighter socket.

http://www.xantrex.com/web/id/186/p/1/pt/10/product.asp

They also have an inverter with a battery included for when you are sitting on aircraft that don't have the in-seat adapter ( like Air Canada, economy )

http://www.preparedwithpower.com/portable/

I have not tried it but it looks useful.