Well, I think that this is a very interesting idea. I'll try to do a resume of the more interesting topics, but of course this list will not be perfect as there have been lots of topics. However I hope it helps you. From now on I'll try to create a post with the list of topics that can be interesting. For this first list I'll see the most read and written topics. I think that some kind of spanish way of writing will be difficult for you to translate, but overall I think you'll get the point of the general sense of every topic.
Puzzleando(the subforum for general topics)
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¿En qué puzzles estamos trabajando? / ¿What are the puzzles we are making at this moment?: In this topic people talks about the development of their puzzles, it's very interesting to see how others makes puzzles, their progress and their ways to make puzzles.
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El fabuloso Guernica / The fabulous Guernica: Guernica is almost the official puzzle of this forum, many people love it and in this topic talk about it.
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¿Cuál es el puzzle más grande que habeis hecho? / What is the biggest puzzle you have ever done?: I must admit that this is a very special post for me, it's the first discussion topic that I posted in 2004. We all know that size doesn't matters but the number of pieces maybe matters
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Objetos con forma de piezas de puzzle / Objects with puzzle-pieces shape: Is your life a puzzle? In this topic you can discover many ordinary objects that have to be with puzzles, from sneakers drawing with puzzle pieces to wooden floor!
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El peor puzzle del mundo / The worst puzzle on the world: Yes, we are used to hear about the best actors, the best teams... but what the hell, we must admit that we all hate some puzzles, here people talks about their most hated puzzles, it's like a therapy
Bricolaje y puzzles(subforum for topics related with all the post-production of the puzzles, such as how to stick them, the conservation and that sort of things...)
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Pegar puzzle / Sticking puzzles: a complete topic about the art of sticking a puzzle. What is the best glue? May the puzzle be damaged? Here there has been a lot of opinions.
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Como hacer piezas perdidas en imagenes / How to make a lost piece of a puzzle: this is a perfect visual demonstration of how to create a piece in case you have lost it and you can't find it or ask for it to the manufacturer.
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Fotos proceso latex acrílico / Photos of acrilic latex process: another classic of this forum, the acrilic latex. I don't know if in Germany it's called by another name but basically it's a product that sticks the puzzle and is transparent and strong enough for using it as the final stick for a puzzle.
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Contrachapado, cartón pluma... ¿Cuál es el mejor?... / plywood, wood... What is best?: it's difficult to translate but this is a survey that tries to show the best kind of wood for sticking the puzzles to preserve them in the future.
Encuentros puzzleros (Subforum for speaking about our puzzle-encounters among puzzlegoers or puzzleros as we say in this forum jeje)
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1º Encuentro: 4.000+2.000 en un fin de semana!! (14-16/3/08): the first encounter, it was thrilling.
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2º Encuentro puzzlero: Madrid, 9/05/08. 8000 piezas y....: the second one, it got bigger...
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3er Encuentro puzzlero: Granada 27/06/08. Casi 10000 piezas: The third one was the proof that this forum was very big...
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IV Encuentro 10-13 Oct 2008 - Cercedilla: here you can find all the information about the last encounter in which we managed to make the biggest puzzle, Life of Educa, 24000 pieces in less than three days!
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V Encuentro en la Rioja del 23 al 26 de Abril del 2009: here is the next encounter, in april, from 23rd to 26th, in La Rioja, land of good wines, if you are interested I'm sure we have place for some english speakers
And well, as I've said I'll try to expand this post to make it a more extensive list of topics for you english/almost spanish speakers
). 
