Need help buying an ATX PSU

I have a GA-P35-DS3L motherboard an an ATX case. Im looking to buy a good reliable PSU that will last me a long time in use as well as future power requirements. Nothing too fancy but not cheap either.

Im aware that buying a good brand is important but what else is important to note down (other than Wattage which hardly tells the full story)?

We will need to know the spec of the pc it will be going in?  A budget? And which country are you in?