Best ab exercise?

1) Can anyone tell me some really good ab exercises? I'm not cutting now, but I will later, I just wanted to know for future reference.

2) I heard crunches were not that effective, that it strains your back.  True or False?

3) How about the ab exercise known as The Plank? Yay or nay?

1.) I like weighted decline sit ups when I do core work, with the option of a twist at the top.

2.) I think it depends on form, I dont particularly like them myself. You know what im talking about the guys that look like there hurling up something and are going to fly off the swiss ball because they have bad form...

and if you do crunch's or weighted crunch's I would do them on the ball.

3.) I like planks, I started just holding it for 45 seconds, then I started adding weight. Put a 45 on your back and hold it there, you'll find out how strong your core is.

I dont do a whole lot of isolations but Ab's and glute ham's (lower back) are things I do to improve core strength, which I think is very important especially when incorporated into the big lifts like Squats, cleans, deadlifts etd...

current 5rm On the texas method
Squat:340
Deadlift:380
Bench:265

currently 233 lb's
goal is eventually a lean 220 play some kind of pro football
Target 40yd time: 4.5

Dude everyone knows the answer to this:

Ab Ripper 2000

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non-weighted?  bicycle crunches.

http://exercise.about.com/od/abs/ss/abexercises.htm

captains chair,weighted decline sit up,weighted oblique work to frame it!done

if you're not continually learning then you're listening to the wrong people!!

-ab wheel is good too
-planks and side planks

I do weighted crunches, weighted planks and side planks.

"In the wild, there is no health care. In the wild, health care is, 'Ow, I hurt my leg. I can't run. A lion eats me and I'm dead.' Well, I'm not dead. I'm the lion, you're dead."

The best exercise is called high intensity sprints and healthy low fat diet. Oh wait that's two exercises.