My battery died recently and took with it my desire to replace it with another clunky, 30lb hunk of battery. So I looked into options for a lightweight battery.
An extremely popular choice is the Deka ETX14. This is the EXACT same 11.5lb battery that Braille sells for $150. At 11.5lbs, it's at least a 10lb savings off any OEM equivalent battery. More important to me though is the size...the thing is TINY! Frees up a whole lot of space in the engine bay. To give you an idea, here's the thing next to a juice box:
Better yet, it can be had for ~$65, which is about the same or less than OEM equivalent batteries. Search around and see what kind of price you can find, but this is where I got mine:
Big Crank ETX14
A lot of places, such as the one above will rebadge this battery with their own name or something but they are all the Deka ETX14.
You'll also need terminals to make the battery work with your battery cables...these are available from Summit Racing:
Summit Racing Battery Terminals
Then, if you want to replace the ugly, clunky, stock mount you can order a fancy aluminum mount from Braille or MMP:
MMP Battery Mount
Braille Battery Mount