Fresh herbs are one of my favorite ways to really enhance any meal or salad. I do grow them but not in the quantity that I use! As such, I am always buying huge bunches of basil, coriander (cilantro) and mint amongst others at my local market. If not stored properly, these are only good for use within 2 or 3 days.
To lengthen the life of your herbs by up to 2 weeks (!!!) here is a very simple trick that keeps them fresh and happy in your fridge.
In a plastic tupperware (or thai take-away container as the case may be) lay your herbs. Cover with a damp papertowl and seal and store in the fridge. If after a while your papertowl gets a bit dry or otherwise looks worse-for-wear, simply replace it once a week. This method also helps stack them nicely to save space. I just got back from holiday and a good week later my coriander (cilantro) is still happy and healthy and enlivening my salads!
Hope this helps!