Seen loads, have a few. I often suspected they were using DDR2 chips as there was briefly a DDR2-400 as well as far as I remember and I've seen chips with the exact same number on DDR1 and DDR2 modules. Cheap no-name stuff it was though, so who knows. I don't know much about the two different types of memory so they might not be compatible that way.

Either way, yeah, BGA chips on DDR1 were used, they worked. I think I actually have seen some SDR with them too.

Edit: Seem to think I bought memory from AData, VData and Integral from Maplin that was made this way towards the end of DDR's lifespan.

I've seen a few, and have a couple right now.
1 is a 512MB DDR333 Registered ECC CL2.5 module, made by Hynix and rebranded by HP
The other is a 1GB DDR333 Registered ECC CL2.5, made by Samsung. In the past I had a few more of these, but sold them. I remember testing them on an AMD760 board.
The 2GB DDR400 Registered modules in my file server are BGA.
It seems BGA is generally more common with the larger sized modules. The ones I've seen have been registered though, I haven't seen BGA unbuffered modules for DDR.

I also have some SDRAM 256MB PC100 registered modules that are BGA. The chips are bare and unmarked with a shiny top surface, like how a GPU looks. The modules had all the chips mated to a thin heatsink. They are branded by HP I think. I noticed that they were using less power than my other, SOIC style SDRAM modules of the same size. They aren't made to be easily taken apart - when I took one of the heatsinks off a few years ago, I realized I had mangled the PCB/chips in the process and ruined it.

SDRAM 256MB SODIMMs for a 440BX based laptop seem to always be BGA, probably because of the physical space. They need 16 chips to work with that chipset, so BGA is the only way to make them. All the smaller SDRAM SODIMMs I've seen were SOIC.

I got one stick of EDO that is like the RDRAM from the ps2 with the exposed dies protected by an aluminum shield, made by Panasonic but none of the part numbers turn anything up in google.

I have some EDO that looks more like the flat, paper-thin, rather wide chips commonly used on SDRAM - it's really realy thin though, more than the SDRAM is.

Also seen SIMM ram with blob chips on it, but only in photos. Not many people seem to have owned computers in this area when that memory was common. In fact, most people I know didn't get computers until 1997 or later, my family were early adopters of such technology compared to the majority.

I also have simm ram here with those called blob chips..