Hm, I think you should´t get a "present" just because one gets a present for engagement in the most common form of a ring. To me this is not a gift as you get for christmas or birthday, but it is a symbol. A symbol as a promise to marry you. In former times it was just a plain ring, but now everyones just outdoes everyone by even bigger diamonds...the meaning of this gesture is totally misunderstood I feel...but certainly there is nothing wrong with it though
so if this is not for you I would consider something that has a similar meaning. I think someone mentioned a ring on a necklace, that is a very nice idea, maybe an eternity band? Or I also love the idea of a Love bracelet. I´m not into common presents like a watch, art, car or whatever was already mentioned. Because as I said, this is not an occasion to get a nice big present, but to get something that has a meaning and can be seen as a symbol of love and promise. Although this is just my opinion, for someone else or you, a "gift" would be more appreciated, I don´t know...
Just as an example, my boyfriend and I were together for ten years this July and he said I could pick a present. Whatever I wanted, clothes, shoes, bag, jewelry...you name it. Although I had an immense wish list I said I wanted an eternity ring with 10 diamonds, even if I don´t wear rings so much. He wash´t into this until I explained why I wanted it. For me this is such a special anniversary and I just didm´t want to have a random present that I could get on every birthday or whatever other occasion. I wanted something with a meaning, something to remember. Even if I could have gotten many things on my list for the price of this tiny but perfect ring, I didn´t want to be selfish with this one...and engagement is something so special, so I really think you could mike your man really happy if you opt for something with the meaning of a ring. Even if it´s not a ring, just explain it to him. I´m sure you will find something that you both love! Sorry for the long text...

Just as an example, my boyfriend and I were together for ten years this July and he said I could pick a present. Whatever I wanted, clothes, shoes, bag, jewelry...you name it. Although I had an immense wish list I said I wanted an eternity ring with 10 diamonds, even if I don´t wear rings so much. He wash´t into this until I explained why I wanted it. For me this is such a special anniversary and I just didm´t want to have a random present that I could get on every birthday or whatever other occasion. I wanted something with a meaning, something to remember. Even if I could have gotten many things on my list for the price of this tiny but perfect ring, I didn´t want to be selfish with this one...and engagement is something so special, so I really think you could mike your man really happy if you opt for something with the meaning of a ring. Even if it´s not a ring, just explain it to him. I´m sure you will find something that you both love! Sorry for the long text...