Since this is a 3E conversion forum I'll assume you're restricting the question to D&D monsters.
What sort of chimeras are you asking about? If you mean chimera in the generic sense of a fusion of different creatures, there are so many in D&D I don't think I could pick a "most interesting" one.
If you're asking about variants of the standard D&D Chimera as a dragon/goat/lion monster there aren't that many.
Offhand I can only think of the Dracimera and Thessalmera - hybrids that combine a Chimera with a true Dragon and a Thessalmonster respectively.
Of those, the Thessalmera is by far my favorite. We haven't done an Enworld conversion for it yet, but its on my to-do list.