Chances are, your partner will be as tired as you are at this time of year, and often the best present you can give is just showing that you care. It's really easy just to buy some lingerie or a DVD or something, but you can do better than that.
For example, you could write a letter that explains exactly how you feel about you feel about her, detailing how proud you are and thanking her for all her hard work and emotional support she's given you over the last year. As long as you don't write it on the back of a beer mat, it'll be something that she'll treasure forever, and it'll make her feel truly special.
You could even make use of our SentForever offer, and send the message into space, so it'll fly through the stars forever.
If you want to give a gift, you can still be quite thrifty - you could, for example, grab a load of tester samples of her favourite perfume from the make-up counter of a department store, and re-fil an empty bottle. Or you could take a photograph of yourself and put it in a home-made frame - even a hand-painted cardboard one will do.