Here is a list from 3 years ago, so it likely needs some updates.
Alliant Powder, Radford, VA (ATK) - Bullseye, Red Dot, Clay Dot, E3, Amercan Select, Extra Lite, Green Dot, Herco, Unique, Blue Dot, 2400, 20/28, 410, Pro Reach, Promo, Steel, Power Pistol, etc. Clays, International Clays, Universal Clays, 700-X, 800-X, made for Hodgdon
St. Marks Powder, FL (General Dynamics) – HP-38/W231, H110/W296, H414/W760, H380, LIL GUN, Hybrid 100V, HS-6, H335, BL-C(2), Titewad, Tightgroup, Longshot, US869, WST, WSF, AALite (WFL), Super-Handicap (WSH), W748, Supreme 780, AutoComp, Silhouette
Thales Australia (Former ADI, now owned partially by French SNPE) – Benchmark, H322, IMR 8208 XBR, H4895, Varget, H4350, H4831, H4831SC, H1000, Retumbo, H50BMG, TrailBoss. H4227 & H4198 both discontinued for IMR 4227 & 4198, which is mfg. in Canada or at ADI.
IMR Powder, Valleyfield, QC, Canada (General Dynamics) – Primary manufacturer of all IMR powder (stick)
Rheinmetall - German Defense Contractor, owner of Nitrochemie. Makes Reloder-17.
Groupe SNPE - French State-owned. Makes all Bofors (most of the Reloder line, and the Norma line), Vihtavuori, and Ramshot powders via their Eurenco layer)