Synths used in top 40 music...

[SteenRNS]

nexus,nexus,nexus

Adventus ,Sylenth ,Vanguard and nexus nexus nexus

[mark1234]

G-Force Minimonsta is 1 that has great basses.

[RaeTheBastard]

Google Synth Secrets, read the whole series.

[Jixxi]

Nexus2, Sylenth and Massive are used very often

[macbeat]

Well depending on the genre it can vary. For most electronic music I'd say Massive. But you brought up Lady Gaga's "Judas" and just so you know RedOne produced all of her tracks using only the synths that come with Logic, so 100% ITB. LMFAO only used Ableton's Operator for every song on their first album. Although trying to get other producers sounds is a fantastic way to learn about synthesis, don't focus way too much on it. By the time you've gotten their techniques down, everyone would've moved on to something else.

But with that being said, I only use Massive, FM8 and Operator. I don't see how I'd ever need anything else since those can pretty much produce any sound I can imagine.

[Resonator63]

Rob Papen Predator