It depends on your girlfriend. Each woman is different so each one has a different answer. What does your girlfriend enjoy or adore? Movies, clothes, books, do these as small present to know that you do like her and constantly think of her.
To show that you really, really care and you plan to be with her for a while you could try these. 1) Buy her a pet, a laptop, a tv, something she loves. 2) Propose. 3) Move in with her. 4) Ask her what she desires in life, then help her get it. 5) Get to know her family.