Future-proofing is a little difficult considering the uncertainty of the future. Your absolute best solution today is a GTX Titan (or two, or three, or four). It has 6GB of effective vram, which is the most out there today. Some may call that overkill, but it's not on higher resolutions. Also, as mentioned, we don't know what the future holds. Hitman Absolution at 2560x1440 maxed out with MSAA x8 uses over 3GB of vram on some scenarios (I know from experience). I'm sure it uses over 2GB at 1920x1080 in those portions of the game. While that's just one game, it's a sample of a game that uses a lot of vram and more could be on the way very shortly. Battlefield 3 uses over 2GB at 2560x1440 an considering Battlefield 4 will be more demanding, expect more vram usage. The Titan is expensive, but it gives you your very best vram option currently and the best potential setup available (4-way SLI with Titans is unmatched).
If you don't want to spend $1,000 per GPU, you could go with a 3GB or 4GB card. I honestly don't think 2GB is enough, even at 1920x1080 (especially if you use AA). There are 4GB editions of the GTX 670 and 680. The HD 7970 and GTX 780 are 3GB cards. If you're willing to wait, I'm sure there will be 4GB editions of the GTX 770 and 780 coming soon. The GTX 770 is currently the price per performance king, so if you're looking at that statistic alone, that's your card (but only has 2GB of vram).