Keyboardists tend to follow a more melodic sound when they go solo. After all keyboards are the most melodic instrument, in Rock music.
(In alphabetical order, by their last name/nickname)
1) Rod Argent (The Zombies)
Originally a member of the Psychedelic Rock band, The Zombies, and later a founding member of Argent, with guitarist and vocalist Russ Ballard. Moving Home is his best solo work in my opinion.
2) Wally Badarou (Level 42)
He also collaborated among other Level 42 members, with the band called M, known for their US #1 hit Pop Muzik. Not so successful as a solo artist, but the one that stands out is perhaps his 12" single, Chief Inspector.
3) Tony Banks (Genesis)
Well, his solo works are mostly film scores, so not much my type of music. Still his work with Genesis was great.
4) Peter Bardens (Camel)
Camel were never as commercially successful, as King Crimson or Yes, unfortunately. Same happened to the keyboardist of this band. Both his solo albums (especially Heart To Heart) and Camel's discography, deserves further notice.
5) Johnathan Cain (The Babys)
First a member of The Babys, where he was in the making of their best album (Union Jacks), and later a member of Journey during their most successful period (Escape, Frontiers). As for his solo efforts, Windy City Breakdown wins. But let's not forget the "cover" of the song Faithfully, in his next album Back To The Innocense (I don't know if we can call it a cover here, because he was a member of Journey too. But the original vocalist of the song was Steve Perry.)
6) Tony Carey (Rainbow)
He played keyboards in the second album of Rainbow (Rising), and later followed a solo career, either using his name or under the alias Planet P. Whilst not successful in his homeland (US), he is popular in Germany, and he is a German citizen as well. His best solo work is definitely the AOR classic, Some Tough City, featuring his only Top 40 US hit It's A Fine Fine Day.
7) Bill Champlin (Chicago)
He was also the founder of a band called Sons Of Champlin, but unlike Chicago they had zero commercial success. His solo works didn't meet any commercial success either, but he became known since he joined Chicago in 1981.
8. Jimmy Destri (Blondie)
He released only a solo album, called Heart On A Wall. It was a commercial failure, missing the Top #200 in US albums charts, but still not a bad effort and it was pretty similar with Blondie's style by the time.
9) Geoff Downes (The Buggles)
A hell of a keyboardist indeed. After The Buggles he joined Yes, for their album Drama, and later he became part of the supergroup Asia. Working with those groups, obviously overshadowed his solo career but he had some very good albums, like The Light Program in 1987.
10) Matthew Fisher (Procol Harum)
Best known for being an organist in Procol Harum, famous for their song A Whiter Shade Of Pale, but his solo career is pretty unknown, yet very interesting. Surprisingly one of his songs (Why'd I Have To Fall In Love With You) is considered a classic in Greece, despite the fact it's unknown in his homeland (UK).
11) Edgar Froese (Tangerine Dream)
A member of the Electronic/Ambiet pioneers Tangerine Dream (and once a member of a Psychedelic Rock band called The Ones), his solo works were similar in sound with his group. Yet not so successful as the works he had with Tangerine Dream, during the 70s.
12) Jerry Harrison (The Modern Lovers)
An original member of the band The Modern Lovers, and later guitarist and keyboardist for Talking Heads. The song from his solo efforts that stands out is Rev It Up. Not a huge hit in the US, but it was a big hit in Australia and New Zealand, which reached the Top 10 in both countries, and the entire album Casual Gods charted well in those countries, especially in New Zealand where it reached #4.
13) John Paul Jones (Led Zeppelin)
Originally a bassist, but a keyboard player as well,and not only. According to Wikipedia: Jones also plays organ, guitar, koto, lap steel guitars, mandolin, autoharp, violin, ukulele, sitar, cello, continuum and recorder. But I had to put him somewhere. Anyway, not fond of his solo works to be honest, but I like the album cover of The Sporting Life, a collaboration with Diamanda Galas.
14) Larry Knechtel (Bread)
Before joining Bread in 1971, he was a famous session musician. His best work as a session musician, would be being part in the making of the album Pet Sounds, by The Beach Boys. Not popular for his famous solo works though, since both solo albums he released, they were commercial failures. Well, not much my style to be honest as well.
15) Kerry Livgren (Kansas)
And the guitarist of the band as well. Also a founding member of the Christian Rock band AD. His solo album Seed Of Change, whilst not commercially successful it's an album that could easily match Kansas' classic albums from the 70s and among the finest albums made by a solo albums. A lost Progressive-Rock classic I'd say.
16) Ray Manzarek (The Doors)
He was also the bassist of the band. Well not exactly bassist, but since The Doors never had an official bass player, so he took the role of the bassist by playing the bass notes on his keyboard. Now for his solo works...not commercially successful as well. His two mid-70s albums, The Golden Scarab and The Whole Thing Started with Rock and Roll Now It's Out of Control, deserve a listen though.
17) Patrick Moraz (Yes)
A guy with an interesting solo career, that could easily antagonize Yes' career. Recommended albums would be, The Story Of I, and Time Code.
18. Alan Parsons (Alan Parsons Project)
Apart from his work with Alan Parsons Project, Alan Parsons was famous as a sound engineer.His most famous contribution, would be the one in The Dark Side Of The Moon, by Pink Floyd. As for his solo career, if you think what was going on in the 90s and how music started to take a downfall, his albums were saving the day. Anyone remember the very good music video of Time Machine?
19) Gregg Rolie (Santana)
One of Santana's original members, and a founding member of Journey as well, where he was the lead vocalist. Still his solo works remain unknown, although his debut self-titled solo album, is one among the many great AOR classics from mid 80s.
20) Ryuichi Sakamoto (Yellow Magic Orchestra)
Although I prefer his stuff with his band, his solo career wasn't bad I'd say. Still he didn't have any success outside of Japan, unlike YMO.