Writing your own editor can be as much fun as writing your own garbage collector.

The "garbage collection" book is the only physical one I still own (everything else given away and in e-form now). It is a fascinating book, and gives you insights into PL run-time systems that you wouldn't get as easily studying other algorithms.

edit: I'm guessing "The Garbage Collection handbook", by Richard Jones et al. Looks like an interesting read.

If you're interested in GCs, I would suggest getting the newer edition for advanced material, and deferring to freely available papers such as Wilson's "Uniprocessor Garbage Collection Techniques" for fundamentals.

And yes, that blue book on garbage collection is worth reading; it's on my bookshelf, too. I'm still looking for something similar on text editors or spreadsheets.