The following spoiler policy applies:
Offscreen (toy-only) characters are not not spoilers. This currently applies to the various Scout Class toys, redecos of toys from the first movie line as other G1-based characters (e.g. Starscream as other Seekers in G1-based decos) and redecos of toys from older lines (mostly store exclusives).
Toys for returning characters who survived the first part unambiguously (Optimus Prime, Bumblebee, Ratchet, Ironhide, Starscream, Scorponok) are not spoilers as long as their alternate forms and robot modes are more or less identical to their appearances in the first movie (i.e. Bumblebee's slightly tweaked Camaro mode), regardless of whether they're new molds, remolds or repaints.
Toys for returning characters who were either implied having died in the first movie (Jazz, Megatron, Brawl, Frenzy, Blackout), or whose fate was left ambiguous (Barricade) are SPOILERS, especially if their new alternate forms and/or robot modes look different from their appearances in the first movie.
Toys for new characters that will make their debut in Revenge of the Fallen are also SPOILERS.
To sum it up, here's the current toyline roster as we know it thus far.
Legends Class - Bumblebee (new mold, 2009 Camaro), Optimus Prime (new mold, still the same truck),
Optimus Prime and Jetfire can combine. This is NOT a fan mode, altough the combined mode looks somewhat awkward due to the limitations of the Legends Class. (select to read)Jetfire (SR-71 Blackbird), Autobot Springer (V-22 Osprey).
Scout Class - Rollbar (delivery truck), motorcycle (possibly "Knockout"), red car (possibly "Dead End" or "Detour"), fork lift (possibly "Scrapper" or "Dirt Boss", based on Scrapper drone from the video game to the first movie), boat.
Deluxe Class - Wreckage (repaint of Wreckage from the first movie's toyline), Bumblebee (remold of Concept Camaro Bumblebee from the first movie's toyline),
Voyager Class - Ramjet (repaint of Starscream from the first movie's toyline), Skywarp (repaint of Thundercracker/Target exclusive "G1" deco Starscream from the first movie's toyline), possibly both store exclusives. (select to read)Soundwave (new mold, possibly a "Preview" figure).
Fast Action Battlers - Double Blade Optimus Prime (new mold), Pulse Blast Bumblebee (remold of Fast Action Battlers Plasma Punch Bumblebee from the first movie's toyline),
Store exclusives - Target exclusive Superion giftset (Silverbolt, Air Raid, Fireflight, Skydive & Airazor; repaint of Enegron Superion Maximus, released in Australia and Southeast Asia in Universe packaging) (select to read)Cannon Blast Megatron (new mold, tank), Jolt (new mold, Chevrolet Volt).