Its hard to pinpoint exactly what, stuff they use live is different than recordings. In the studio Wayne Coyne, Michael Ivins, and Steven Drozd all share bass playing. Each one of them uses a different bass tone. To me alot of the recordings sound like a 50 or 100watt tube head turned up pretty good. Otherwise Michael Ivins plays bass most the time live and i think he is a big roland/boss fan. Some stuff here on this
thread
which mention these boss pedals, from a bass player magazine interview
boss odb3
boss bf2
boss syb3
boss syb5
Otherwise their is lots of interviews with the lips about what they use in the studio, i did a quick search and found
this
a few really fun videos of them in the studio
Heremuch more fun to listen and watch.
Otherwise The Flaming lips have a great collection of music which spans many years, Clouds taste metallic and At war with the mystics are my favorite. But pretty much all the albums will grow on you. Pink robots and Embryonic get stuck in my head all the time.