Much of what I learned about Golden Age/early Silver Age Superman and Batman came from these two tomes. I was constantly checking them out of the library until I managed to find copies of my own:
I picked up the new Batman Encyclopedia a couple of years ago and it doesn't even compare to the original. It has more illustrations, including a lot of color pin-up pieces. But the majority of the black and whites are just scans from the comics and aren't converted to line-art like in the original Fleisher encyclopedias. In addition, the new version seems to want to cover all of the confusing history the Dark Knight has gone through over the years, including multiple versions. What I liked about the Fleisher books was they tried to write it as though it was one character who had gone through changes and not different versions of the character over the ages.
My only disappointment in the Fliesher books was their info stopped around 1964 or so...
There was a Wonder Woman volume too but I've never had the chance to read/pick -up one of those: