The Legend of Zelda-For obvious reasons...
Halo-Halo is an amazing franchise with a large universe and great story telling with a cast of awesome characters. Halo is more than just a shooter and I think that needs to be recognized (especially around here). Halo has some of the better music in video games and beautiful environments to look at with great level design. Not only did it revolutionize gaming twice, but it continues to be innovative with each game.
Resident Evil-This is the definition of survival horror. The first five Resident Evil titles were really great because of the formula they used. You had to back track and use your brains as to where to go next or what item goes where. The camera angles were also something really amazing about the first 5 titles. You never knew what was around the corner. Sometimes, all you'd just hear things and not want to continue knowing that you have to face something. Part of the reason I'd be reluctant to encounter enemies would be scarce ammo. You never had enough. Each game also had some very cool surprises that kept the games feeling fresh and scarier each time. Then comes Resident Evil 4 and 5. The more action heavy titles. Resident Evil 4 was more action packed and did change the formula completely, but you were still alone facing hordes of enemies. The atmosphere was still very creepy and the locations were just spot on. Years later we are treated with Resident Evil 5 which was not scary at all but very intense. It continued the series with a great story but really didn't contribute to the horror aspect in which the games are known for. And now, just a couple of months away we are going to be treated with what seems to be the perfect balance between horror, action, story, and puzzle solving. Resident Evil is just a really amazing series with a perfect cast of characters.
Some honorable mentions would be Gears of War, Mario, Splinter Cell, Assassin's Creed, Grand Theft Auto, and Metroid.