Skipping over some favorites that got mentioned already:
Arturia Buchla Easel V – I don’t have a real one for comparison, but this sounds and behaves exactly like I’d expect one to. I don’t use it as much as Aalto, but patching it informed my “real” modular patches.
Plogue Chipsynth PortaFM – lovely, painstakingly recreated Yamaha OPLL. If I learned anything from modular, it’s that 2-op FM is better than 4-op or 6-op 
Audio Damage Ratshack Reverb – I love its retro psychedelic twanginess. I like layering it with more realistic (heheh) reverb.
AudioThing Fog Convolver – the first IR reverb I’ve used that’s stable, has a decent GUI, doesn’t impose lots of latency and isn’t too expensive.
Toneboosters Barricade 4 and EQ 4 – my go-to master bus plugins that sometimes get thrown into group busses too.
U-He Presswerk – my “this needs a little more love during mastering” compressor.
Sonic Charge Echobode and Permut8 – for somewhat weird and really weird delays, respectively
Voxengo MSED – I’d kind of like something better, but this one is free and I use it all the time for mid/side processing with modular.