In my view the 1995 E300D is under appreciated and they could be found at reasonable prices. I bought mine with 86K miles and put 30K miles on it with no troubles. The 95 was the last year of the W124 bodystyle.
The 98-99 E300D turbos are nice but quite expensive. Another car to consider is the 300E 2.5 turbo which started in 1987 or so. 84-85 300Es are great too. Suppose it depends on your budget and preferences.
In terms of forums I like the Diesel discussion forum at shopforums
http://www.mercedesshop.com/shopforum/forumdisplay.php3?forumid=15
There is also a good listserv that talks about diesel powered Benz's.
Chuck