Considering your background (ZooPlantMan) i will estimate that you are interested in the design of the exhibit more then the group dynamics. I've seen quite a few european elephant exhibit's and each and every one i've seen are barren.
Only Burger's Zoo in Arnhem (the Netherlands) manages to keep some trees alive in their elephant exhibit but the rest of the ground is barren again. Still, seeing elephants in the tree shades gives a REALLY nice feel about the exhibit and makes you feel that this is how asian elephants should be displayed, under tree canopy's.
The Elephant Houses are sometimes huge (Cologne) or very well decorated (Hamburg, Rotterdam, Leipzig) but always relatively empty for the elephant, except for a pool. Many zoo's however still keep them on rather small fenced or moated outside area's with small boxes per individual inside (Amsterdam, Liberec, Prague, Krefeld).
Worth mentioning would be Amersfoort Zoo who purposely build a completely seperate Bull-barn. It's the biggest building i know build for one single animal and for just a bull, it's very nice consisting of a large sleeping area with sand and a small area with concrete where they can do things like training, pedicure and take blood. Their female barn is about to be replaced by new one in 2010, building will start end of this year.
The only exhibits i would estimate worth seeing and not barren are Beauval, Benidorm and whipsnade. Perhaps one of the Aspinall's parks as wel, but that would be it. Copenhagen and Parc Paradisio (Belgium) are building a new elephant exhibit and Prague, Poznan? and Planckendael (Antwerp's open range-zoo) are planning new exhibit's, perhaps you could get your hands on some of their idea's?