What are the Must Have addons?

I'm new to RW3 and to this forum. I'm an old MSTS user from way back, but just got RS2012 a few weeks ago. I've been having a blast. I just discovered Railworks America this week, and have been reading and looking. I do love American railroading the most, although exploring the other routes in RW3 has been a lot of fun.
So, I've been looking around a lot, and I've installed the two free scenarios from the RRYard, and Smitty's Default Duties. I've just bought the Donation Rollingstock package for the R&WA (and downloaded the other freeware rollingstock packages along with the MC&SA route necessary for Footeforward's scenarios). Looking forward to getting that and trying it out.
But my question -- driven by my long time use of FSX and the knowledge that there are some addons that are just "must have" addons, like pretty much anything by A2A, and the scenery of Orbx -- what are the addons that should be at the top of my list for US railroading? Payware or freeware. I've been looking hard at AllAboard's Ohio Steel and his Kent and Eagle Lake routes. I'm looking at the Portland Terminal. But those are easy to spot, sitting on the Steam DLC page. What are the ones I don't know about that really should be on the top of my list? The best and most enjoyable addons? I like freight more than passenger, but I like it all! Of course, I'm needing those packages that work with TS2012 now, as we all are.
Thanks for any help pointing me in the right directions.
Phil
So, I've been looking around a lot, and I've installed the two free scenarios from the RRYard, and Smitty's Default Duties. I've just bought the Donation Rollingstock package for the R&WA (and downloaded the other freeware rollingstock packages along with the MC&SA route necessary for Footeforward's scenarios). Looking forward to getting that and trying it out.
But my question -- driven by my long time use of FSX and the knowledge that there are some addons that are just "must have" addons, like pretty much anything by A2A, and the scenery of Orbx -- what are the addons that should be at the top of my list for US railroading? Payware or freeware. I've been looking hard at AllAboard's Ohio Steel and his Kent and Eagle Lake routes. I'm looking at the Portland Terminal. But those are easy to spot, sitting on the Steam DLC page. What are the ones I don't know about that really should be on the top of my list? The best and most enjoyable addons? I like freight more than passenger, but I like it all! Of course, I'm needing those packages that work with TS2012 now, as we all are.
Thanks for any help pointing me in the right directions.
Phil