1. Kratos: Actually there
2. Sweet tooth: Ice Cream and Machete on the ground where guy is sweeping
3. Fat Princess: Cake on the ground where guy is sweeping
4. Sly Cooper: Staff hung up in hallway on left when she firsts enters
5. Colonel Radec: Gun in hallway on the left right before she unlocks the door
6. Parappa: Beanie on the floor where guy is sweeping
7. Nathan Drake: Actually there
8. Big Daddy: HIs footprints on the ground in the hallway
9. Spike: The sign where she is typing references ape escape, forgot what it says and too lazy to look back on it
10. Heihachi: His sandals on the ground in the hallway
11. Toro: White cat under the car in the beginning
12. Ratchet & Clank: Letter girl is typing is in his game's language
13. Jak & Daxter: Drake's license plate thing is in his game's language
14. Sackboy: Actually there
15. Dante: His bullets scattered where the guy is sweeping (if you have played DMC you know those are his because there is so many, who else has that many bullets)
16. Raiden: His sword hung up on the right side of the hallway by heihachi's shoes
17. Nariko: Heavenly Sword hung up. Seen abocve the girl as she walks out the room after typing the letter
18. Sir Daniel: His sword on the left side of the hallway by big daddy's footprints
19 & 20. Cole & Evil Cole: Cole is actually there.
Predictions: Heart tatto on her hand shown when she uses the key to unlock the door may be Kingdom HEarts, so Sora. The snake on her dress has to be MGS so snake maybe. If you have any others feel free to add.
Actually, the hint for Dante is in the postcard on the womans desk that says "Limbo City".