In New York, Ric Ocasek introduced Rivers to his guitar collection, from which three guitars got heavy use on the record: A red 60's Fender Jaguar, a 1955 (according to Ric, but it looks like a '59 to me...) Gibson Les Paul Junior Special, double cutaway, and another Les Paul Junior Special, in yellow [not pictured] Here they are, with Jasons Telecaster (more on that later) between them.
The Gibson (above) is definitely one of the finest
guitars ive ever seen, and its sound is unbeleivable, responsible for a lot of the sweet crunch found on the blue album. both of the Les Pauls would later return for the Green Album, though by this point Rivers heavily favored the yellow one. [
see Green Album section]
Also responsible for that
sound is the Mesa Boogie, which was still in top condition at this time. The
Mesa was run through the tall Marshall, often at unusually low volume, to get
some of the sounds on the album. As far as I know, there are NO effects pedals
on the guitar sounds on the Blue Album. Rivers would not start really fooling
around with recording with effects and pedals till later...
Rivers also picked up an acoustic guitar at this point, and brought it to Electric lady, where it is heard on the intro to "Jonas" and "In The Garage". This was a 1974 Gibson. I dont have the exact info on this at the moment, but I know it was either a J-45 or a 70's descendent of a J-45. It sounded amazing. Sadly, this guitar was to meet a tragic end later, when Rivers had his leg brace. The brace wore a huge hole right through the bottom of the guitar, which Rivers duct taped together for a while. The thing still sounded pretty good in this state, but it didn't last. The guitar was either trashed or given to Justin Fisher [ of Shufflepuck, Nerf Herder, and Psoma ]. I'll have to check with Justin on that one.

Note that the acoustic guitar shown inside the blue album cover is a Yamaha F-310, which is a basic, cheap, decent sounding guitar. This guitar is not the one heard on the blue album, and I'm not even sure whose it is, or if it still exists. It isn't likely to be Jason's, as this photo was taken after Brian joined the band, but it is possible its one of the several acoustics that Jason played in the band in the earliest weezer days, before he went electric. (see Jason's section)
Keyboards on Buddy Holly: In 1993, a friend was storing his late 80's digital synth at 'the garage' where weezer practiced and cut demos. This was a Korg M1 type synth, definitely not vintage or cool in any way, especially then. But it had a huge library of sounds, and in between the koto drums, etc, Rivers stumbled across a slippery little sound that he decided was just right for his new song "Buddy Holly". Later, in NYC recording the Blue Album, Rivers tried in vain to get that same sound from different equally digital synth that was brought in. For whatever reason no one could find the same model as the one back in L.A. The sound used was basically as close as Rivers could get it to what was on the demo.
Harmonica on Jonas; In The Garage: info coming.