Other World Computing has been a go-to site lately while researching the pros and cons of upgrading to a solid state drive, with plenty of easy to follow videos showing not only the performance differences, but more importantly, how-to instructions for upgrades in memory, hard drive capacity and cloning/copying files. The OWC Blog is also a great resource (and marketing tool) for those who like to read about optimization tips and general tech/Mac news.
The site can be a bit overwhelming if you're not acquainted with tech catalogs, with a sort of shotgun blast of product images and specs that can be a bit daunting. But once you find what you're looking for, OWC tends to offer information beyond price/specs, with instructional info and tips generally not included by other suppliers.
Prices generally are close or the lowest available, but we're prone to pay a little more knowing their products were thoroughly tested as an actual Apple Certified Developer. The company assembles and sells its own line of hardware products under the Mercury brand here in the United States, so if you like buying "American", this might be a plus.
And to lay on a little more love, we commend OWC for earning a LEED Platinum Certification by the Green Building Certification Institute for their Illinois headquarters. Platinum is the highest achievable level of the LEED (Leadership in Energy and Environmental Design) Program, which began in 1998; OWC also became the first privately owned light manufacturing/assembly building in Illinois to obtain LEED Platinum status. They even have their own a Vestas V39-500 kW wind turbine to provide energy on-site. If that's not geeky cool, we don't know what is.