Just start with the easy ones,those who are kind of "famous"
You may probably know them but that's ok
Caravan,Camel,Renaissance,Gong,Amon Dull,Tangerine Dream,Gentle Giant
You could check some unknown bands here
http://www.progarchives.comAnd someone's else list with the best prog rock albums ever...
I will put it here to find it easy and check some albums too
ELOY "OCEAN"
ELOY "SILENT CRIES AND MIGHTY ECHOS"
NOVALIS "SOMMERABEND"
GROBSCHNITT "ROCKPOMMEL'S LAND"
NEKTAR "REMEMBER THE FUTURE"
YES "TALES FROM A TOPOGRAPHIC OCEAN"
JETHRO TULL "A PASSION PLAY"
YES "FRAGILE"
BIRTH CONTROL "BACKDOOR POSSIBILITIES"
VIRUS "REVELATION"
MY SOLID GROUND "MY SOLID GROUND"
TRIUMVIRAT "SPARTACUS"
PINK FLOYD "ANIMALS"
QUEEN "A NIGHT AT THE OPERA"
THE ALAN PARSON PROJECT "EYE IN THE SKY"
GREATFULL DEAD "BLUES FOR ALLAH"
IRON BUTTERFLY "IN A GADDA DA VIDA"
MARILLION "MISPLACED CHILDHOOD"
KING CRIMSON "IN THE COURT OF CRIMSON KING"
GROBSCHNITT "RAZZIA"
AMON DUUL II "YETI"
THE MOODY BLUES "LONG DISTANCE VOYAGER"
ANYONES DAUGHTER "ADONIS"
BIRTH CONTROL "OPERATION"
PINK FLOYD "THE DARK SIDE OF THE MOON"
HAWKWIND "IN SEARCH OF SPACE"
NEKTAR "JOURNEY TO THE CENTRE OF THE EYE"
IQ "DARK MATTER"
ARENA "PEPPERS GHOST"
DREAM THEATER "IMAGES AND WORDS"
QUEENSRYCHE "PROMISED LAND"
MAGMA "MEKANIK DESTRUKTIW KOMMANDOH (.M.D.K.)"
MAGIC PIE "MOTIONS OF DESIRE"
KANSAS "SONG FOR AMERICA"
STYX "PIECES OF EIGHT"
GENESIS "FOXTROT"
GENESIS "SELLING ENGLAND BY THE POUND"
ELOY "DAWN"
PINK FLOYD "WISH YOU WERE HERE"
PORCUPINE TREE "VOYAGER 34 -THE COMPLETE TRIP"
KALACAKRA "CROWLING TO LHASA"
NEU "NEU"
NEU "NEU 2"
ATOMIC ROOSTER "IN HEARING OF ATOMIC ROOSTER"
TWENTY SIXTY SIX AND THEN "REFLECTIONS!"
GRAVY TRAIN "STARCASE TO THE SUN"
ANDROMEDA "EXTENSION OF THE WISH"
SUPERTRAMP "BREAKFAST IN AMERICA"
GENTLE GIANT "POWER AND THE GLORY"
JETHRO TULL "HEAVY HORSES"
JETHRO TULL "AQUALONG"
TOOL "LATERALUS"
PSYCHOTIC WALTZ "A SOCIAL GRACE"
THRESSHOLD "CRITICAL MASS"
MEMORY GARDEN "TIDES"
MAGELLAN "IMPSSIBLE FIGURES"
PENDRAGON "THE MASQUERADE OVERTURE"
NOVALIS "BRADUNG"
EMBRYO "OPAL"
FATES WARNING "A PLEASANT SHADE OF GREY"
EMERSON, LAKE AND PALMER "TRILOGY"
APHRODITE'S CHILD "666"
SOFT MACHINE "SIX"
CAMEL "SNOW GOOSE"
CAMEL "MIRAGE"
A PERFECT CIRCLE" MER DE NOMS
ANGRA "HOLY LAND"
SAVIOUR MACHINE "LEGEND PART 1"
MAHAVISHNU ORCHESTRA "VISIONS FROM THE EMERALD BEYOND"
AL DI MEOLA "ELEGANT GYPSY"
RETURN TO FOREVER "ROMANTIC WARRIOR"
WISHBONE ASH "ARGUS"
URIAH HEEP "MAGICIAN BIRTHDAY"
ANATHEMA "ALTERNATIVE 4"
PAIN OF SALVATION "BE"
SAVATAGE "HANDFUL OF RAIN"
TRIKOLON "CLUSTER"
QUEEN "QUEEN"
MIKE OLDFIELD "OMMADAWN"
ROXY MUSIC "AVALON"
RICK WAKEMAN "RETURN TO THE CENTRE OF THE EARTH"
THE BEATLES "SGT. PEPPERS LONELY HEARTS CLUB BAND"
OPETH "DAMNATION"
DEATH "INDIVIDUAL THOUGH PATTERN"
PETER GABRIEL "SO"
FAUST "IV"
PAVLOVS DOG "PAMPERED MENIAL"
POPOL VUH "NOSFERATU"
TANGERINE DREAM "RUBYCON"
THE FLOWER KINGS "THE SUM OF NO EVIL"
PINK FLOYD "THE WALL"
ELOY "POWER AND THE PASSION"
ELOY "INSIDE"
NEKTAR "A TAB IN THE OCEAN"
BARCLAY JAMES HARVEST "GONE TO EARTH"