ROB, Duck Hunt, Mr Game and Watch, Falco, and the Mii Fighters have all been confirmed as upcoming Smash Bros Amiibo. Additionally, Nintendo of Europe's official site slipped up and gave us a glimpse of new Mario Maker and Animal Crossing Amiibo that have yet to be announced.
Back to official news, Nintendo announced Street Fighter's Ryu joining Smash Bros as a fighter, as well as Roy from Fire Emblem. Ryu for either version of the game will run you $5.99, or get him for both versions for $6.99. Included with that purchase is a new stage from Street Fighter, Suzaku Castle. Roy is available for $3.99 for either version, or $4.99 for both Wii U and 3DS packaged together. Both character DLCs plus the previously announced Lucas are available now (for $3.99/4.99). Eventually, all Smash fighters will have corresponding Amiibos.
More paid DLC announced today includes new costume for the Mii fighters, and the Dreamland stage from N64. If you want all of the DLC Nintendo announced today, it'll cost a total of $21.96 for either or $29.16 for a Wii U/3DS bundle.
There's also a new free Miiverse stage available today, and "Tourney mode," which will come out for free in August.