Depends which direction in music taste you're going in, but if you're looking for hugely powerful contemporary VSTs, then you want to check out stuff like Xfer Records Serum, UVI Falcon, Parawave Audio Rapid, VPS Avenger.
If you want more specialized stuff, then Native Instruments Reaktor (analog & hybrid modular), Absynth (dreamy drones/pads/samples), Kontakt (industry standard sampler), FM8 (DX7 On Steriods), Monark (Minimoog emulation) will cover most of your needs. You can get them all in NI Komplete if you want to save on money, especially wait for Black Friday sales for 50% bargains.
If you care about sound quality, then consider u-he ACE, u-he Diva, u-he Repro, u-he Zebra 2 and Synapse Audio The Legend for circuit modeled emulations. LuSH-101 already covers all your high quality Roland type sounds, while for Roland Drums consider D16 Group's various drum emulations, or AudioRealism Drum Machine. For more Roland stuff, consider the high quality but expensive Roland Cloud.
Then there is Arturia, which is increasingly becoming better and more powerful, but very retro orientated with their Legacy Collection, which is currently at Legacy V Collection 6 with 21 instruments.
My personal picks would be Serum [Wavetable Synth], Absynth [Sample Synth Madness], ACE, Diva, Repro, GForce Oddity 2 [Analog Modeled], Arturia DX7 [FM Madness], Arturia Synclavier [Additive, FM, Resynthesis Synth], Image-Line Harmor [Resynthesis Madness].
No rest for the wicked.