There are a variety of alternatives for the standard AR-15 buffer spring. Some of the alternatives include braided springs and non-metal springs. Armaspec offers a product called the Stealth Recoil Spring that replaces both the buffer and spring.
The Stealth Recoil Spring, or SRS-1, is a self-contained unit that is designed to be a simple drop in replacement. The unit has multiple stages (it looks like two in the photo, but could be more internally) to slow the bolt carrier group and reduce felt recoil. In a way, it looks like it operates the way some of the other recoil springs on the market (like the Gen4 Glock pistols) work.
According to the company, the Stealth Recoil Spring has an added benefit of not rubbing the side of the buffer tube (aka receiver extension) when you are shooting the gun. Armaspec advises that this product should be ready to ship in the first quarter of 2017. Currently, the company expect the SRS-1 will carry a suggested retail price of $79. It is not known if there will be different models to replicate different weight buffers or if the assembly can be adjusted in some way.
Armaspec currently makes a variety of other AR parts and accessories including stainless steel replacement parts (buffer retainers, detents) and the Rhino magwell grip. The company also has plans on making an ambidextrous charging handle called the Victory. This charging handle is projected to cost $70, but no shipping date has been offered.