Above are three astromech units from TCW series, left is R3-S6 aka "Goldie" and right is R2-D2, both of these figures I've posted before, however center is R4-P17, Obi-Wan Kenobi's astromech during the Clone Wars.
On the right is R4-C7 from an ARC-170 star fighter set I have that I have yet to post.
Left of this text is another R2-D2 figure, this is the one I use in my Yavin Medal Ceremony diorama, what I didn't show off before was that this is actually a ROTJ inspired model that has a button on the front to make Luke's lightsaber pop out the top as R2 does on Jabba's sail barge.
This figure is based on the original concept art for R2-D2, I have more figures in this series and will post them all in the near future. As you can see R2's design didn't change a great deal but I'm glad they decided against the arms.
On the left is the R2-D2 figure I use with my Dagobah X-Wing, interesting feature on this model is that it plays R2 sounds and the photoreceptor lights up (the light only ever flickers, getting a decent photograph was a nightmare).
Lastly here is a simple group photograph of all seven astromechs, without whom doors couldn't open, starfighters couldn't fly and death star plans couldn't be sent.