HyperParse. I based my ParsePro program on this. It is full featured and works fine, but lacks some of the power of ParsePro [imho]. Still a cool stak, and I suggest that if you ever need something to parse your text, and find ParsePro to be unsuitable, then try this.

HyperTalk QuickRef. This is a really good stack that goes beyond the simplicity of the HyperTalk Reference and gives you a good quick list of every command and function in Hypercard, including the ones that the Reference left out, such as the "answer folder" option, among others. It's not perfect as it's interface requires just a little bit of work, imho, but other than that it's pretty much perfect.

PolyButtons. This stack uses some scripts that are placed in your button to make it seem to be a polygon. This is great for a lot of uses, and so the stack gets a good review. However, things do slow down a little when using polybuttons, as it takes a bit of time to calculate whether the click was inside or outside the button. Still, it's worth a look at.

Quit The Finder. This little thingy makes the Finder quit when the stack it is installed into is opened. This is great for older computers where ram is very limited, and could also allow you to extend Hypercard as a sort of AtEase-type program.

Random Sentances. This powerful and advanced stack produces random sentances based on lists of possible words it has in various cards. It works surprisingly well, and could be a good starting point for building a language stack that produces random sentances in foreign languages, even if that language (e.g. Indonesian) uses different syntax and word order. It doesn't earn a full Classic award, because of the damn annoying beep each time you generate a new sentance.

Del MerryXmas. This stack hunts down and destroys the MerryXmas virus, the first Hypercard virus. The virus can be dangerous to your stacks, and if you want to download anything Hypercardy, I strongly suggest you get this, as once infected, you're in trouble. This can also make your stacks immune to the virus, so once you've downloaded it, you can happily leave your stacks alone with no thought as the virus. It should make use of a GetMultiple xfcn to allow you to select multiple stacks at once, but as it is, it works fine.