Maureen Gilmer of the DIY Network recommends these tools for every gardener -- aspiring and otherwise:
Clippers -- Probably the most-used tool any gardener can have, clippers are a very personal choice. Clippers need to fit your hand, so you may have to invest in several pairs before finding the ones that are right for you. They are a very good investment -- a well-cared-for pair should last you for around 20 years!
One warning about clippers: They are one of the easiest ways to spread diseases such as black spot and fire blight from one plant to another. The best way to prevent this problem is to get into the habit of disinfecting your clipper blades after each use. To do this, spray the blades with a mixture of one part bleach and three parts water; leave it on a few seconds, then wipe off. Dry the blades with a paper towel or a rag, then add a few drops of corona oil to seal the blades and prevent rust.
Pruners -- These are essential for heavier jobs, but their size and weight can make them very tiring to use. Make sure when you're shopping for pruners that when they are completely closed, there is no chance of your knuckles hitting one another.