Quite a few, in my opinion. Here are six, off the top of my head:
1. Discipline 27 II
2. The Soul Vibrations of Man
3. Astro Black
4. The Antique Blacks
5. Voice of the Eternal Tomorrow
6. The Sound Mirror
These are all very solid Ra albums in my opinion. (Some Ra records can be aimless unless you're a hardcore fan.) Atavistic was on schedule to reissue Continuation, but it never materialized. Anyone know what happened? Between the Unheard Music Series and Art Yard, Ra reissues are still trickling out.
Of the six titles listed above, I consider Discipline 27 II a true Sun Ra classic. This one is trance-like at times.
I go with this list, and would add "Universe In Blue", "Unity", and "My Brother The Wind, Vol.1". The latter has seen a vinyl reissue a couple of years back.
"The Antique Blacks" was released by Art Yard on CD and LP last year:
http://www.flyglobalmusic.com/fly/archives/europe_reviews/sun_ra_the_antique_black.html
http://lightintheattic.net/releases/459-the-antique-blacks
http://boomkat.com/cds/245287-sun-ra-the-antique-blacks
'The Ridiculous "I" and The Cosmos Me' must be one of the better song titles ever.