Very hard and the list would change from day to day, but I'll limit myself to ten here:
Bil Evans Trio: 'Explorations'.
Van Morrison: 'Astral Weeks'.
Tim Buckley: 'Starsailor'.
Bob Dylan: 'The Freewhelin'.
John Coltrane: 'First Meditations'.
Love:'Forever Changes.'
Marvin Gaye: 'Here, My Dear'.
Bunny Wailer: 'Blackheart Man'.
REM: 'Murmur'.
Bert Jansch: 'Rosemary Lane.'
Charlie Parker: 'Charlie Parker On Dial'.
Roy Harper: 'Stormcock.'
Well that's 12! Fairly representative but I've deliberately ignored the less well-known stuff.
I've got quite a few rare records, but as a collector, that's pretty much to be expected. Lots of original British and American psychedelic mono lps, a fair few original mono Blue Notes, some rare 60's folk, jazz and blues albums. Examples:
Pink Floyd first two albums in mono.
Nick Drake originals Island pressings.
Jimi Hendrix Track originals mono and stereo.
The Who: 'My Generation.' mono Brunswick.
Traffic: 'Mr Fantasy mono.
Blossom Toes: 'We Are Ever So Clean' and 'If Only For A Moment.'
All Beatles, Bob Dylan, The Who, The KInks, Small Faces, Pretty Things and Rolling Stones monos.
All Doors, Jefferson Airplane, Love, Quicksilver and Grateful Dead monos
Dexter Gordon, Jackie McLean, Lee Morgan, Sonny Rollins, Art Blakey, Wayne Shorter original Blue Notes.
Late 60's/early 70's British jazz originals: Tubby Hayes, John Surman, Mike Westbrook, Ian Carr-Don Rendell Quintet etc.
Lots of Prestige and Riverside labels jazz originals: Paul Chambers, Bill Evans, Red Garland, 'Trane etc. The most I've paid was a couple of years ago: £160 for a mint copy of Trees 'On The Shore' lp.
The record that I would pay the most for is an original copy of Tina Brooks 'True Blue' Blue Note album. which is wonderful and impossibly rare. Drugs, alcoholism and shabby treatment by Blue Note did for him, but he is probably my favourite saxophonist. There's a reissue due some time soon. The whole album is on youtube. I promote Tina whenever I can. Genius.
Bargains? Lots of rare late 50's/60's records in VG condition with tatty sleeves that I've cleaned and they sound ok if not perfect. The Doors 'Waiting For The Sun' ( £10) in mono springs to mind as does a mono of Dexter Gordon's 'Gettin' Around'. (£5 years ago) Lots of ECM originals for £3 or £4. Lots of Creation and 4AD label stuff ( £10 or so) ( House Of Love, Cocteau Twins, Lush, Primal Scream etc) which will hopefully rocket in value!
I do like new music but I tend to listen on youtube or buy cds. If I find copies of recent Jonathan Wilson and Sufjan Stevens records, I'll snap them up but I don't buy online. My daughter has all originals of Joanna Newsom and The Smiths so she's got the bug too. God help her.