This is a tough one, as while modern forks are better in almost every way, some retro forks were very good for their time.
My favourite and regretfully sold retro fork is the Judy fsx. Looks great and worked really well stock, but was improved by either adding springs, slapping in Judy DH cartridges for rebound and compression damping, or the icing on the cake, ecko sport air dampers. Swapping out the stock brace for a carbon stuff one and the ti bolts from a Judy sl to take it to another level. You could go even further and go for an after market crown too. Judy Sl or DH too.
Other great forks were givin/noleen carbon crosslinks or as someone has mentioned, amp f3 or BLT.
An overlooked fork imho was an rst xmo. Lighter and stiffer than a sid, with ecko sport air damping.
Never had a set, but liked the look of and sound of the manitou efc.
Another sold regret was a lawwill leader 3.
I've always heard good things about marzocchi bombers, bomb proof and reliable plushness for their day.
Sid's were nice but flexy.
Not sure of the timeline but pace rc36 in various guises, the evo3 with ti nitride uppers looked great, the red eddy Irvine edition was cool looking too. The pro class 2 was also a nice fork, and rc38 air force, though these may all have been later.