I have started to use E.ggtimer.com, for one-off reminders for doing something in Xmins or similar.  I wanted an easier way to quickly get a timer for an undetermined amount of time, so I whipped up this bookmarklet: E.gg Timer.  Now, with just a click on this bookmarklet, I am prompted for the time, and it then opens a new window with the E.ggtimer started.