I had a PNY memory card that I gave to my daughter. No problems with it to date. I use SanDisk and Lexar. I'm not sure of the warranty on PNY, but if you have problems with SanDisk or Lexar, they often repair or exchange the card without question and with no charge if there is a problem.
Make sure all things are equal. If your SanDisk is an ultra II, I recommend that you keep it. It is a high speed card and the extra speed is much better when shooting video at full resolution and frame rate, and when shooting in continuouos mode. If you've paid $90 and it is not a high speed card, in my opinion, you've paid to much.
My 1 Gig Ultra II was $100 from Amazon, but I also got a $20 rebate. Memory cards are frequently discounted, at least in the U.S. where I live.
Related reading: Memory cardshttp://www.digicamhelp.com/memory-cards/index.htm