Congratulations. I have a Sizzix cutter and have found that the heart, circle and star dies are the most versatile. I have a few leaf ones which are good as well.
The heart can be made into flowers and leaves - (especially the long,skinny heart shapes). The stars can vary the flower shapes as well and it is always difficult to cut accurate circles, so they are very handy. I bought butterflies and dragonflies which I don't use often. There is a teardrop shape which has been useful for flowers as well.
A good set of the Alphabet could be handy if you like using letters on your quilts. I bought one set, but have never used it!