QUOTE(Harddisk @ Jun 4 2010, 11:43 AM)
While we are at it, can anyone tell me how many design are there for the basic RX-78-2 Gundam? I've seen similar designation but with different shoulder armor design. Why is that?
Not sure what you are asking, but here goes:
For gunpla...
MG - 1.0, 1.5, ver Ka, Perfect Gundam, OYW, ver2.0 (these are not including MSVs)
HGUC - original, 30th anniversary
Not sure about ancient versions of gunpla, and recolors/extra-finish/special editions don't count.
As for in-universe RX-78s,
RX-78-1 : Black and white unit
2 : Amuro's red-white-blue unit
3 : G3
4 : The blue one with beam launcher
5 : The red one with gatling
6 : Murdoch
7 : The Katoki designed one with full-armor parts.
Note that Murdoch is the only one without any mainstream gunpla released. There are also variations such as Casval custom and the recently released FA gundam. The Alex is loosely based on the RX78 series although it's often considered as a separate unit.