Re: 6600GT or 6800LE
I would skip both and get the 6800nu. The 6600GT is about $200, good price for the performance, but you gave the 6800LE as an option too. The cheapest 6800LE I have seen is about $260. That was off of
http://newegg.com. The cheapest 6800nu I have seen on newegg is $270. I would definitely opt for a 6800nu. And if you don't mind me suggesting one, I would go for the BFG 6800OC. Roughly half of them are unlockable (I have one and it's unlocked). Unlocking does NO damage to your card. If the pipelines don't work, then no worries. Just turn 'em off and you've still got a great card. Here, also, is a link of my 6800nu unlockable chart.
http://hardwareanalysis.com/content/topic/33402/
I highly recommend a 6800nu over a 6600GT or 6800LE. It has more staying power, with the 12 pipelines, and with the good chance of unlocking the other 4. If you have any questions on unlocking the pipelines,
http://www.guru3d.com is a good source to read from, and me and mothow both have unlocked 6800nu's. Good luck with your decision!