The Bioenno Power LiFePO4 batteries seem to be very popular. They are lighter, per amp hour, then the sealed lead acid batteries. They also have a slightly higher voltage then a SLA battery.  But, they are more expensive than SLA's  LiPo batteries, as used in model aircraft, are also good choices but the amp hour capacity is very limited. They are very small in physical size, great for backpackers and perfect for QRP radios. 

When it comes to cost per amp hour, I found the LiFePO4 battery to be the best alternative:

LiFePO4, 12v 20ah