You can start with the list at https://lmms.io/documentation/Tested_VSTs
Synth1 will get you a long way. I use a few other DSK VSTs like Overture, Indian DreamZ and World StringZ. I also use Dexed (DX7 emulation) but it is a bit unreliable in LMMS. Oh and a couple of odd ones...Delay Lama (http://www.audionerdz.com/ ) and Plogue's AlterEgo (https://www.plogue.com/products/alterego/ ).
Steve