MAN has a great viewing area,the Aviation Viewing Park although its a short bus ride/drive from the terminals! Actually at the airport the top level of the multi storey car park gives a good view if you can't make it to the Viewing park!
has a good observation deck at T2
& I believe they still do ramp tours! Unfortunately the better T1 deck has been closed for a couple of years now & nobody knows if it will reopen!
Most German airports seem to have a viewing area/observation deck at the terminals,TXL
the list goes on!
has a small terrace between the piers but a better view can be had from the top of the multi storey car park behind the terminal!
has a viewing terrace at both T1 & T2
also has a good viewing terrace.
doesn't have a official viewing area but most spotters gather behind the Benetton shop(near McDonalds) in T2
which gives great views over much of T2
both runways & I think a bit of T1? Although the police here can sometimes be a bit of a pain in the a*se!