With trip music, there are a few directions to go for me.
A) Familiar Music With Nostalgia Factor - Nothing makes you feel warm and cozy and gooey inside more than tunes that you have very positive memories associated with. This is obviously different for everyone, but can include otherwise cheesy music, youthful favs that actually suck, show tunes, as well as your all time favorites... the song playing on your prom night slow dance, Disney style cartoon music, that worn out cassette that you listened to on a loop in your walkman etc.
B) Atmospheric Music & Uplifting Sounds - This stuff is great to set a vibe and not overly demand your attention. Stuff that transforms the fabric of the soundscape and injects good vibes. Indian Classical Music, Dub Reggae, Ambient, Baka Pygmy Music, Aborigine Didj Stuff, Tibetan Throat Singing with Bells, Renaissance Madrigals, Brainwaves layered with Nature Sounds, even some New Age stuff. It doesn't have to be backgroundish, but can simply raise the vibration and create feelings of love, light, divinity etc. It might not be stuff you would normally dig either. Gospel is AMAZING. Ravel's Bolero will blow your mind. Shimshai's Suddhosi Buddhosi or All That I Am. A little Bob Marley never hurts...
C) Really Complex Music Which JAMS HARD - This includes the usual suspects. Jam, Prog, Krautrock, Jap Acidrock, Fusion, Jazz-Rock, Space Rock, Canterbury etc. Some purely electronic music can qualify too. Dubstep & Psytrance... some Goa. The most intricate Classical Music fits here as well. The main thing is that there is some jaw-dropping virtuosity to go with the jaw-dropping visuals. Hyperspace beings love the virtuosos, and will come out to chill with you if you play them some sick ass shit. They are not impressed with most pop drivel or seriously repetitive stuff. Even stuff that is great for dancing at a club often makes them smirk. Hit them with something like Billy Cobham's Quadrant or Steve Vai's Tender Surrender or For The Love Of God... Primus... They really dig the impossible Chopin piano pieces. The Rock from Rachmaninov. Even stuff like Steely Dan's Bodhisattva and The Grateful Dead's The Eleven. Ozric. Zappa's Guitar Jams. John McLaughlin. Soft Machine's Hazard Profile. Stuff like Pink Floyd's Echoes... Rush's 2112 or Xanadu.
D) Music That Makes You Wanna Cry - Believe it or not, these sad songs are often gold. They are direct from the heart, and this quality of soul makes them epic when you're out there. Otis Redding, Donny Hathaway, Joni Mitchell... the gut wrenching stuff from Ben Harper. You know the shit. Blues.
Anyway. I am sure you all have your own philosophies about this. Some music hits two or more categories and gets bonus points. Looney Tunes Jazz from the 30's & 40's is SICK. (Carl Stalling was a GENIUS). A lot of music from that era works like gangbusters. Speakeasy, Ragtime, New Orleans. Hard to have a bad one with Louis Armstrong or Sidney Bechet playing.