A more complete Response for Rim
1st Expansion -
Desert of Flame only becomes necessary when you reach lvl 40-45. Lots of 45-60 content there but not much else so you dont need to worry about it until you get there.
2nd Expansion -
Kingdom of Sky comes bundled with EQ2 now. Mostly high end 55-70 content however it also contains Achiement Points (AP) which can be gained starting at lvl 20. AP help customize and pimp out your character so its nice to have KOS right off the hop.
Expansion 3
Echoes of Faydwer comes out in November. Adds new race and city.
Adventure Packs - mini expansions available for digital download that cost about 7.99 each. Not necessary, just a means for SoE to profit.
Advenure Pack 1 -
The Bloodline Chronicles. Basically a 35+ instance/quest hub featuring vampires. For 7.99 you get a couple instances and access to some neat items that drop.
Adventure Pack 2 -
Splitpaw Saga. Much more useful than Bloodline Chronicles. An instance hub/quest hub again. With a twist. Scaleable instances. If you go into an instance at lvl 20 the monster/ item drops are all lvl 20. If you go in at 45 its lvl 45. Same instance. Lots of solo content, including solo instances. lvl 20+ content.
Adventure Pack 3 -
Fallen Dynasty comes out in June. More high end content. Instances, quests, fear, crafting etc.