If you are not going to get a factory battery I would go with an
Interstate Megatron.  Other people recommend the Optima gel filled
battery.  If you are going with a cheapie go with Autozone or Checker or
Kragen or Pepboys as they will honor the warranty without too much
hassle.  If you go with Wal Mart be sure to keep the receipt.  If you
don't they will not honor the battery.  I took my nephew to get his
battery replaced at Wal Mart and they would not honor the warranty.  The
kid hd lost the receipt.  The battery was not even a year old.  I would
not go to Wal Mart for this reason.  The other places I mentioned keep
your information in their computer so if you don't have the receipt you
are covered.  And, did I mention that the Wal Mart battery only last a
year?  Your choice...

batteries are like anything else.

you get what you pay for

I suggest getting an Interstate