Since they were the first fish I bought for the tank, I should introduce the platies first. My first purchase was a group of five "sunset coral dwarf platies". I asked for 2 males and three females (they recommend 2:1 female to male sex ratios for platies), but turns out the guy at Petsmart couldn't tell a female platy from a male and I ended up with four males and one poor female...who was very pregnant from the start. (I don't have any pix uploaded, but this is a picture of sunset coral dwarf platies).
As I mentioned before, I returned to the petshop a few days later and got 3 more (female) dwarf platies, and one (female) "mickey mouse platy" which looked something like this one. Shortly thereafter the first female had babies, and a day or so later I noticed major fin rot on both her and the "mickey mouse" platy. Without knowing what to do, I separated out the sick fish...and they died overnight. But after a 10% water change and an increase in temperature, the rest of the fish were ok. Since then, and especially now since my second water change, the male platies are going crazy, trying to mate with everything else (including the Corys). The females (and the second largest male) are looking pretty harrassed. Two of the females are huge with babies - the smallest (and fattest) female is ridiculously large.
And then there are the real stars of the aquarium - the platy fry. But I've said enough about them already.