There are so many brilliant tools out there for shaping sounds - the widespread availability of top-notch plugins for mixing and sound design has never been better, or more affordable. Whether it's an emulation of a classic piece of gear, or something totally unique, a new plugin can inspire new creativity and help you to refine your personal sonic signature.
That said, I really think that on the whole, you can easily make a top-class mix using stock DAW plugins; but there are some things out there that *may* do something different, or simply work in a way that you are more comfortable with. And there is still nothing better that nailing a sound "at source" via great recording technique!
Here are my 'Desert Island" plugins, then: ones I use on 99% of my mixes currently. In honesty, I don't use many more than this - I know these inside out and can get so much out of them. Some are well known; some less so. Have a read, and feel free to chip in in the comments!
SLATE DIGITAL "VIRTUAL MIX RACK"
I know, it's a bit of a cheat... in reality this is more of a suite of plugins. But as it takes care of a lot of the sonic heavy lifting in my mixes, I just have to include it.
Slate's Virtual Mix Rack (or VMR) is like a plugin version of the best 500 Series rack ever. You get a ton of great tools in here - some of it modelled versions of classic gear (Neve/SSL/Urei/Empirical Labs etc) and some that are more custom-designed to achieve a specific task (like the excellent Bomber).
The thing I love about this is how complimentary each of these effects are to each other - I have uses for all of them! The Neve EQ rules for broad tonal shaping, the SSL EQ for more precise cuts; and the filters on the Custom EQ are things of beauty! Likewise the different compressors each have a clear sonic signature that can give alternative levels of dynamic control and tone shaping, whether or not they nail a specific piece of gear (clue: I don't care).
VMR is also part of Slate's subscription service, which includes a raft of other brilliant plugins (including delays, reverbs, tape saturation and mastering limiters). This is a super affordable $15 per month, and would be my first recommendation for anyone looking to upgrade on their DAW's stock plugins.
KUSH AUDIO "NOVATRON"
This is a particularly brilliant compressor. Kush writes that Novatron is, "an analog-modeled compressor that borrows so many sonic properties from so many different classic hardware units that, ironically, it could only exist in the world of DSP". At its' heart is a modelled tube compressor/limiter not unlike the wonderful Fairchild 670, but with a much wider range of control and adjustable input and output transformer saturation. It also has a selectable sidechain (which you can either key off of an exterior source such as a kick drum or use as a low frequency control) and parallel blend.
Most importantly, it sounds GREAT. There's a lot of value within this compressor; I use it on kicks, percussion, vocals and often over the whole mix. The thing I love about it is you can really dial in the tone you want - it'd be a great plugin to learn compression on, as you can hear the changes you make very easily. It's very similar to working with hardware in this respect.
Like Slate, Kush offer a subscription service full of amazing virtual gear for $9.99 a month. Check it out, and watch some of their videos too - real informative stuff.
GOODHERTZ, INC "VULF COMPRESSOR"
Yes, ANOTHER COMPRESSOR. But I promise it's worth a place. This thing is an absolute beast! Developed in conjunction with Jack Stratton of Vulfpeck, the Vulf compressor gives a totally unique take on compression: rubbery, crunchy, gloopy and tons of vibe. It is absolutely NOT a transparent, cold bit of gear! I love it on drums, guitars, piano (especially piano) and it's super fun to mix into if you want a mix that really moves. Aparrently its inspired by the Vinyl Comp on the Roland SP303 sampler, but has been totally expanded on.
I am a big fan of the design of this - it's not made to look like a bit of hardware, and the way it works is a bit different to most compressors. I feel this really rewards experimentation, and not just falling back on "default" settings (10-to-2 on an 1176, anyone?). Magic stuff.
Soothe is a multi-band dynamic EQ that seeks out resonant frequencies and tames them. It's like having a ton of intelligent notch filters that react to the nasty stuff in a sound source. It is easy as pie to use, and it works like a charm! Stick it before compression to stop the compressor reacting to the wrong frequencies. Put it on the 2-bus and it helps translation to different speakers etc. Use on vocals to cut out shrillness when a singer starts to belt, or to remove boominess on acoustic guitar.... There's a good argument to use this thing on every channel of your mix. A total Swiss army knife, and one that is guaranteed to make your mixing better.
GOODHERTZ, INC "TILTSHIFT"
Another one from Goodhertz, and a different take on EQ. Tiltshift is a 'tilting' equalizer - one that can take a sound source and simply make it brighter or darker without otherwise affecting the tonal balance. It does this using DARKE MAGICK (I think), Brilliant for mastering - if a mix sounds a little bass heavy, you can fix it. I often put it on the 2-buss of my mixes after compression to gently bring top end back. It's great for adjusting for proximity effect on close-miked sources too.
I love Goodhertz. I trialled all their plugins, and ended up buying most of them. As mentioned earlier, they have a unique design, and they seem to approach the usual tropes of compression/EQ/saturation/modulation from a fresh angle. Go look into them. I could have included Lossy and Wow Control in this list too....
VALHALLA DSP "ROOM", "PLATE" & "VINTAGEVERB"
$50 each, valhalladsp.com
Yeah, I cheated again... not sorry. In reality any of these would be a fine purchase, but I use all of them so frequently it's impossible to choose!
Whether you're looking for clean, realistic spaces (Room), lush and modulated ambience (Vintageverb) or rich and classy reverberation (Plate), Valhalla have you covered. These reverbs do all the sensible stuff - short room ambience, drum chambers, vocal plates... but they all go much further than that too. Brilliant for sound design, these verbs have control over every possible parameter and maximum decay times between 30 seconds and almost two minutes!
They just sound beautiful, too. I know that convolution reverb has the edge for 'realism', but realism and reverb are totally opposing ideas. Whacking ANY reverb on a close-miked snare doesn't sound like that snare in any room in the world, so let's forget about making it sound real and just focus on making it sound good, shall we? (Rant over).
A freebie! This thing lives at the end of my 2-bus chain and NEVER LEAVES. Span is a customisable FFT frequency analyser. It's super accurate, very easy to read, scaleable, free.... It's not sexy. It dosn't do anything, except allow you to check that you are hearing things accurately. Even sat here in my purpose-built control room, I use this every day. Brilliant for comparing the tonal balance of your mix to a reference track and invaluable as a sanity check after a long day mixing. Go get it!
So, there you have it. These are the plugins I couldn't live without. They all suit my workflow and my personal sonic signature in a way that I feel is essential. You may well find other things that work better for you - that's all part of the fun! You can get trial versions of all of the paid plugins, so give them a try and let me know what you think.