Gravedigger, Allard's Wolfhound, Gertrude (go 1st Kestrel Grenadiers!), Jamison's Stalker, Klatt's Awesome, Shin's Hatamoto (one of the more interesting ways to get in to canon), Trish's Shogun, Sawyer and Vandergriff's Banshees. As Martius mentioned, a lot of MW versions (or based on MW versions) got added in (MAL-2R, AS7-S3, some Catapults, Dragon, Hatchetman, Centurion, Hunchback...I think those are all based on MW/MC) . Updated versions of the old dual cockpit 'mechs. JM7 series Jagermechs. Some long missing variants (CPLT-K3, TBT-3C, STK-6M). And variants based on notes in the technical readout (the panthers that swap their er ppcs back to ppcs, orion refits, quickdraw refit, the wolf dragoon's mechs (back to the intro tech versions since they didn't go in 3039 and the Klondike versions). A couple Starterbook: Sword and Dragon variants got placed in RS3050Uu as well (Zeus, Wolfhound, Firefly).
Wolfhound Allard - Daniel Allard, Kell Hounds, from FM: Mercenaries
Centurion Yen-Lo-Wang - Kai Allard-Laio, 10th Lyran Guards, from Blood Legacy, et al.
Caeser Archangel - Marcus GioAvanti, Avanti's Angels, from Double-Blind
Caeser Gertrude - Hannah McQuarters, 1st Kestrel Grenadiers, from TR:3050U
Grasshopper Gravedigger - Aaron Pollyea, NAIS / New Avalon Cavaliers, from TR:3050U
Orion Kerensky - Aleksandr Kerensky, SLDF, from Battlecorps
Awesome 9Ma - Adam Steiner, 1st Somerset Strikers, from 1st Somerset Strikers
Awesome Klatt - Rodney Klatt, Crescent Hawks, from TR: 3050U
Hatamoto-Chi Shin - Shin Yodama, Izanagi Warriors, from Miniature Rules
Shogun Trisha - Trisha Ryoko, Wannamaker's Widomwakers, from TR: 3050U
Stalker Jamison - J. Elliot Jamison, Zeta Battalion, from Last Days of Zeta Battalion (Battlecorps story)
Banshee Sawyer - Trent Sawyer, Bronson's Horde, from TR: 3050U
Banshee Vandergriff - Victor Vandergriff, Solaris VII, from Illusions of Victory