Just like all of you have been mentioning, poetry is the usual genre for bilingual editions, mostly because editors and translators realise how much cannot be truly rendered from a language to another. The endless lyrical resources that make poetry be poetry practically disappear from a language to the other, unless a certain work bumps into a very artful translator who can come up with effective ways of making the new language convey the same or similar aesthetic bliss as the original one.
This last thing sounds brilliant in theory, but unfortunately, it often ends up in actual verbal entaglements that give readers in other languages false impressions about certain works. For example, the average reader of the Divine Comedy in Spanish will probably have the idea that Dante's masterpiece is much more inaccessible and unreadable than the average reader of the Commedia in English. This is because almost all translations of it in Spanish attempt to keep the terza rima, causing the tercetos to have the appearance of having been trapped inside a tornado (words are added, removed, mixed up and so simply to keep the form).
To sum up, all these titanic translation tasks (usually unavailing) can be avoided either by bilingual editions or really good prose ones (that's how I read the Commedia and the Odyssey; accepting of course that something is always lost in translation).
I tend to agree with Tomwk. For bilingual/parallel text books I actually prefer current titles vs. classic literature. I discovered book that's written about Spain (and of course bilingual Spanish-English), Los Secretos Mejor Guardados de España/ Spain's Best Kept Secrets. It's great if you're planning a trip to Spain or simply want to daydream about that spectacular country...in English or in Spanish!