So I guess most people have at least glanced at the survival mode by now but if not you should. I have to say it is more than I expected. I haven't quite figured out my startegies because there are tons of levels but I have some ideas.
I think one thing that cannot be overlooked is claymores. Not only can you get 10 at a time but you can buy 10 more immediately after use the previous 10. A huge advantage over zombies 2 claymores per round. When planting make sure to place them far enough away from each other as to not blow each other up. I usually plant them in a path and then lead the enemies through the same path. Seems to work better than camping one spot with a whole bunch of claymores.
Predator missles are also a must in later rounds. While you can use bullets to take down choppers and kill juggernauts, missiles do it in one shot. If it is not a juggernaut or chopper round I usually use a missile at the start of the round. This way it gets huge groups of enemies instead of 2 or 3. I wish you could carry more than one missile strike at a time though.
Delta squads and riot shield squads are good but I have limited use of them.
Feel free to add your own strategies.