Optima Batteries RedTop Battery
I had to replace my Impala's original battery in 2007 and the best replacement I could find was from Optima® Batteries.  I've been very happy with the new battery ever since; it has no problem starting my car even in the cold winters we get here in Utica, NY.  These batteries are solid lead-acid and are otherwise drop-in replacements for the original batteries. 

I found that swapping the batteries was a gigantic pain in the back-side.  In order to get at the battery, you need to remove the passenger-side diagonal chassis brace and the cover to the fuse box.  There are two bolts that secure the battery into the holder which can be difficult to reach properly without some good extensions and a u-joint.  Finally, physically maneuvering the battery out of that compartment is a very tight fit.  You'll definitely want to remove the fuse box (secured by two nuts to the strut tower) to make some room for yourself to work in.

One web site that I researched estimates that it would take more than 45 minutes to get the job done.  It's certainly accurate that it took me more than 45 minutes to swap the battery the first time (and several pain relievers to help with the resulting back pain the next day).  These batteries from Optima Batteries are a little smaller around the sides (that is, they're not a box with straight sides).  As a result, they're a little easier to get out than the original batteries.  I'm waiting for somebody to successfully remote-mount their battery and write up how they did it.