I hope they avoid the mistake of multiple villains. The Harvey Two-Face plot felt forced in the last one. Two villains just brings back memories of the last franchise. If you want to add something to a singular villain, you can always have a good henchman or two. Alternatively, you could have one primary villain with perhaps another character with a personal score to settle with Batman (perhaps The Joker left a disciple behind in the form of Harley Quinn?).

One thing they should consider is flash-forwarding several years. Let Wayne Manor and the bat cave be fully rebuilt. Let Gotham have recovered from the Joker, who has been locked up in Arkham for years. But show that Bruce Wayne is still haunted by the showdown.

As far as villains go, everyone seems high on The Riddler, and I think he could be a solid foe. But I also think a very dark take on The Penguin would be intriguing, though possibly a bit much following up on Ledger's intense performance as The Joker.

Now might also be a good time to introduce Vicky Vale as a love interest. Perhaps Scarlett Johanssen, who worked with Bale and Nolan in The Prestige?

Yep, I agree on the multiple villain mistake. That's why I'm kind of worried about Iron Man 2, but we will see. I love the direction of flash-forwarding. Maybe The Joker is still locked up in Arkham, but we never see him and can just feel his presence throughout the film.

Exactly (re: Joker). It's a great way to deal with the loss of Ledger (who knows if anyone will ever even come close to being able to replicate that role) while preserving one of the most iconic figures in all of comics. I love the idea of simulating his "presence" over Gotham. That's why I like the idea of a Harley Quinn type character, though that also starts to drift into "Saw" territory.