A great online stopwatch and countdown especially designed with big buttons for tablets and mobiles, although it works perfectly well on computers as well.
http://ictmagic.wikispaces.com/ICT+%26+Web+Tools
"This is a really good way of testing out practical measuring skills in Maths lessons.
I always teach 'measuring' by incorporating a Harry Potter themed Potions lesson. Pupils follow potion recipes to create potions from the Harry Potter universe, e.g. Polyjuice Potion or Skele-gro. I have a mixture of powders (cornflour), plants (herbs) and potions (water with food colouring). I then have pipettes, a range of different containers with different scales for measuring liquids, scales for measuring the plants and powders, in addition to gloves for handling the 'poisonous' plants, a pestle and mortar for the plants and stopwatches for timing."
A simple, elegant html timer site with a stop watch, count down and alarm clock. Click at the bottom of the screen to customise the background and choose a YouTube videos which will play for the alarm or when the count down has finished.
http://ictmagic.wikispaces.com/ICT+&+Web+Tools