I am posting a list of some of the best vst plug-ins that electronic musicians would really need.This is not a full list of all vst's you need,but it's a good beginning .Some of them are free ,others not,but consider having at least some of them.Here is the list:
VST Plug-in (instruments)
1.z3ta+ this is an AWESOME plug-ins and one of the must-have's.
2.Pro-53 The next must-have.Really powerful,one of the best for making leads.
3.Nexus Contains some really nice presets.Very good for hardstyle,hardcore,trance,dance and others
4.Microtonic Very good drum machine vst
5.FM8 contains very good sounds.Appropriate for electronica/idm and every other genre.
6.Junglist pretty useful,too.
VST Plug-in (effects)
3.Dblue_glitch -free and pretty nice.Can make miracles with beats
4.Devastor A powerful distortion plug-in
5.Guitar Rig Don't get confused with the name,it's not for guitars only .
6.TriDirt good EQing and distortion enhancer plug-in
Hope this could help you.