This week I found out that smart phones, including the one I already have, are fast enough to emulate all kinds of systems. My Galaxy Note II makes a great DS. I've enjoyed reconnecting with the games I once loved, and the one's that I missed out on. I tried a Pokemon game for the first time. It's not for me, but it was fun to try.
The DS emulator I'm currently using is DraStic. It cost $6, and it was totally worth it. It's actually better than a DS in some ways, because it's customizable. Plus you can just save at any time without relying on the in game save system. You can also turn up the speed when it's convenient.
I've only downloaded games from coolrom.com, and I highly recommend them as well. They even work with dropbox.
I definitely feel obligated to pay for any game I decide to go through, but there is no technically acceptable way to do that. I plan to just buy the games, and stick them on the shelf. I don't feel the need to buy any game that I'm just trying.