Check raising is a VERY valuable tool for getting maximum value out of your big hands against bad and average players in NL. The check raise bluff is a very good play against good, tight players (and if you're caught they'll know you're capable of a check raise bluff and so you can pull off some nice value check raises against them).

Fnord has the right idea about bluffing in No-Limit--it's disastarous when playing against good observant opponents if you never bluff because you'll get no action on your good hands. On the other hand, if you go charging in full steam playing for your stack blindly hoping they'll fold you're setting yourself up for a lot of destackings. The best way to get an action image without putting a lot of your chips at risk is to make a lot of small and medium sized continuation bet, scare card, and semi-bluffs.

I find the semi-bluff is a very useful tool in NL and I use this play A LOT (I semi-bluff draws virtually every time if the pot is unraised or I raised preflop). The expressed and implied odds combined with the folding equity make it a greatly +EV play and I've won lots of big pots when my neatly disguised draw connects.

Save your big bluffs for when you have a strong read that the other guy can't call, and I would recommend showing your lousy hand if your bluff succeeds to generate action later. Also remember, bluffs don't have to work close to every time to be +EV, just enough to justify the pot odds (i.e. potsized bluff has to work at least 1 in 2 times to be profitable, 1/2 potsized only has to work 1/3 of the time to be +EV.