I didn't really recommend anything, LOL
in freebies, try the following:
simulanalog.org pack (oldies but goodies, I actually like the 900 simulation's spring reverb a lot and use it to mix, usually to distort and spring up digital echoes on a return buss where I feel too lazy to hook up my tube PA head and tapco spring reverb and mic the speakers). I find myself using the DS1 a lot on synths. Slapping it on a 303 insert sounds just like a 303 into DS1 and a DI. No joke. Why spring for a pedal I would only use on synths? The univibe isn't too bad either. These pedals aren't pretty though, they just use your DAW's native GUI
the poullin plugins are good for overdrive, mostly heavy amps like bogner and a 5150 but there's an 800.... not bad overall, really excel at dirt, less so at clean and that just breakin' up tone. But that's a tall roder. Nothing quite like real tubes.
excite amps does a bunch of tolerable stuff for free, I haven't sued much of it but I have all their stuff
there's this thing called amplion that's supposed to be a mesa rectifier.... I've used real rectos and I think the plugin sounds better for guitar LOL the spring reverb on it isn't bad and its a pretty cool plugin for adding grit and vibe to DI or software synths but its high on CPU for how little it does
look for acme bar gig's 'shred', the amps don't sound right but they sound interesting and the room simulation engine seems to be based on impulse responses. The sound of the cab sim and room sim together is surprisingly cool. Its kidna nice to disable the guy's amp simualtions and just use his cab and ambiance engine. It can help DI clean guitar sit in a mix. Its a low CPU hit for how good it sounds too but like I said, most of the amps sound a bit weird to me and the effects built in are junk.
if you can find them Distorque makes KILLER vintage stompbox plugins and a cool rack chorus that has a tri-chorus vibe. I was really shocked at how cool their fuzzface/tonebender sounds. Youc an go under the hood of all their plugins and adjust virtual component types and values too. I still own a fuzzface and have owned tons of them as well as tons of tonebenders, a buzzaround etc. These guys got the magic of those old fuzzes. Its insane. But all their stuff is good.
for more quality stomps look up TSE, they do a rat, a tubescreamer etc. The rat is their best one.
that's all I can think of off the top of my head.