16GB and 32GB models: something of a given, really; flash memory prices are still dropping, and Apple's habit ever since the first iPod nano has been to double capacity every year. It's the main reason I'll probably be upgrading my iPhone this year.
HSUPA 3G access: Infineon should have a new HSUPA chipset ready in time for an iPhone to use it, so that's what I'd expect. You'll get somewhat faster downloads, but the main deal is better uploads. Don't even think about HSPA+; there'll barely be any access points in 2009.
iPhone firmware 3.0: you know how background push notification still hasn't shown up yet? My hunch is that they're saving either that or true background apps for a major firmware revision to launch alongside the new iPhone. Hopefully there's also copy and paste as well as turn-by-turn GPS nav, but regardless, I get the feeling there'll be something big.
802.11n Wi-Fi, video chat, others: ...are big fat "maybes." HSUPA is better for video chat, but ideally you'd wait until the lower latency of 4G (LTE) to do it. There are mobile 802.11n Wi-Fi chips now, but it's a tossup as to whether or not Apple will have access to them.
And now it's your turn.