Building a 100 album vinyl collection 3 must have albums are?

lately, it's 

A Day at the Races

Let it Bleed

His Band and the Street Choir

There are absolutely no "must-have" albums. None, zero, zilch.

Find three albums that YOU like, that is all that matters. If you don't know what you like, wait, buy nothing. Find out what YOU like and then get those.

I like to support new artists on Bandcamp, so possibly head over there and take the plunge. Most of it is not my taste, so it takes a bit of time to try a bunch of different artists/bands/genres. Occasionally, there may be some unexpected happy surprises. Good luck with your journey of music discovery!

1.  Fleetwood Mac Rumors

2. Dire Straits Brothers in Arms

3. Pink Floyd Dark Side of the Moon

4. Miles Davis Kind of Blue

5. Matchbox 20 Yourself or someone like you

6. Al Stewart Year of the Cat

7. Johnny Cash At Folsom Priso

How about anything that Mannheim Steamroller ever recorded? Some of the best vinyl in my collection of 2k albums or so. Does anyone listen to them anymore? I never see them mentioned. American Gramaphone did vinyl as well as anyone.

Telarc, 1812 Overture, and Crystal Clear Virgil Fox organ music also great recordings, classical music. Also Canadian Brass on Umbrella Direct to disc is excellent.

Dire Straits Brothers in Arms also a good suggestion. 

Most any Alan Parsons as well. Great recordings. 

Heart, Little Queen

Emerson Lake and Palmer, self titled

Fleetwood Mac, Rumours

Madonna, Ray of Light, German pressing

Tori Amos, anything on vinyl, colored or clear vinyls better than black copies that I have. Great voice, great recordings.

Enya, nothing I've found by her has disappointed me. Even her CD's are good.

Pat Benatar had a great voice and did some great records. Tropico is probably my favorite.

Linda Ronstadt, Heart Like a Wheel, One of the best female voices ever and a great recording. A little country twang at times but damn good. 

Cat Stevens, almost all. Island recordings better them A&M. I have 6 copies of Tea For the Tillerman and the best is on Island. 

Whenever possible, originals are almost always better than re-masters, at least in my experience. For those of us in the US, imports from the UK, or just about anywhere in Europe are better than the US, second and third generation stuff.

Much would depend on personal taste. I never listen to jazz so no help from me there. 

I don't have a TT, but I know a few that I would buy immediately if I ever did get one.  Jackson Browne Running on Empty would be one and so would Bruce Sprinsteen Darkness On The Edge Of Town.  Someone already mentioned Linda Ronstadt Simple Dreams and Cowboy Junkies Trinity Sessions, so although they would be on my personal list, I won't list them.  Did anyone list patricia Barber Cafe Blue?  That would be my third pick.  But there would be way more than 3 . . . some by Dire Straits and some by Steve Earle. . . .