extreme III 30 mb/s is the best card considering price to performance ratio and it's speed is enough for 99% of the situations
if you are thinking faster card allows me to shoot more fps, then if you do the math you will see that the gain is not that much
considering you will shot 8fps and your buffer is 16 frames, then you will fill the buffer
in 2 seconds... now the speed difference between sandisk III and IV is approximately
around 6 mb/sec, so those two seconds will give you one more frame to shoot
so if you need to be able to shoot more frames, then it's rather worth spending your money upgrading the d3 buffer than buying extrteme IV cards
Choose you camera and see the actual performance numbers.
But I agree the 30mb/sec Extreme IIIs are the best deal with rebate til mid Septmeber. 3 - 8gb cards for $164 and they send you an $80 prepaid CC. The Exteme IV's aren't a bad deal either $342 for 3 cards with a $200 card. But I never had any card related issues with the older Extreme III cards and the new ones are faster so when I just upgraded I didn't bother with the IV's.
I now use exclusively TRANSCEND 8gb (own 10)....have 2 Lexar 2gb fantastic cards but Transcend does as good as Lexar or SanDisk and is usually a whole lot less expensive.......I purcahsed 6 of my current 10 Transcend 8gb cards for 15.99.....now they are between $29 and $79.......so I can get a 16gb card for less than 2 8gb cards............
All brands of cards fail.........it is just a matter of when....not if.........so I have a great recovery software from Lexar that recovers all the current raws, jpgs ..........