Most people would consider Sportscard Guaranty Corporation (SGC) the 3rd most popular grading company, after PSA and BGS. Based in Florida, they have been around since 1998, and tend to be a more economical option than the big 2 and their ‘Tuxedo’ slab is preferred among a number of collectors.
SGC operates with a 10 point scale with 2 levels of 10, Pristine basically being a perfect card, and Gem slightly less than perfect. SGC also features half point grades from 1.5 to 9.5.
The company does have tiered pricing based on declared value of the card being submitted for grading. That said, the maximum declared value of the lowest tier is significantly higher than PSA ($1500 vs $200), and CSG doesn’t require a membership to get the lowest price.
SGC seems to be much more popular among the soccer/futbol collecting community.
All of their graded cards have a serial number so you can track the validity of graded cards on the secondary market, now with high-res images, and they have a population report on the website.