Mass Effect: Stardust
While most corporations follow morally-dubious tactics at the best of times, they present to an enterprising mercenary a means to a large amount of money, and possibly a personal military outfitter. Being a company man may prove a rather enticing proposition.
Corporations are able to be many things to PCs: allies, enemies, sources of agreements, missions, contacts, or leads, and even patrons. They represent an endless font of opportunity and are likely going to make their need for groups of all shade of Reputations or motivations known to the PCs.
The corporations listed on the main wiki page are those offering an arsenal of sorts for purchase (and thus are more likely of interest to PCs for their catalogues), but other corporations may become only an employer, and not a supplier. They will show up in the Organizations section, though may stray into others (such as Enemies) over time.