www.travel-dealz.de: a very active blog listing all kinds of travel deals, including hotels, economy and business tickets and also occasional train deals. Focused on Germany, Austria and Switzerland, but also listing attractive deals elsewhere.
www.travel-dealz.eu: the English language sister website of the resource above. Allows you to choose a particular region or country for deals applicable to that part of Europe. Also lets you subscribe to a daily newsletter with the latest deals. Will send you an immediate message when there is a spectacular deal.
www.insideflyer.de: this website also consistently publishes attractive business class fares.
www.insideflyer.co.uk: this site publishes occasional business class deals.
www.thepointsguy.co.uk: the UK sister of the originally US based website is basically a credit card selling channel, masked as a travel blog (as many frequent flyer sites). Nothing wrong with that (well, until you've seen interest rates on UK credit cards).
www.secretflying.com: I basically stopped monitoring this site because of its annoying navigation and its tendency to plug error fares (which, contrary to what they claim, have very high odds to be cancelled).
What to expectThe best business class deals for South-East Asia (Bangkok, Kuala Lumpur, Singapore) are from 1,000 euro return with a decent airline. The deals to wait for are Lufthansa/Swiss' companion offerings (appearing all over Europe in no apparent pattern), Qatar's special sales (though increasingly rare).
If you're looking for first class, your best bet is a Lufthansa/Swiss companion sale. These occur from Saint Petersburg, Moscow, Kiev, but also from more approachable cities such as Oslo, Stockholm and Milan. The lowest fare you'll find will be just under 2,000 euro. If you're heading for Dubai, you might even pay just over 1,500 euro.
The best fare I ever found to New York was 800 euro (from Dublin) years ago, but I've never been able to replicate it. Fares go as low as 1,000 euro for TAP flights via Lisbon originating in Scandinavia, and for La Compagnie flights from Paris. There are regular sales from various alliances starting at 1,200 euro.
If you want to experience a 'real' business class, there are only few intra-European options. The best value one is LATAM between Frankfurt and Madrid, which you can book from an amazing 150 euro return including lounge access and priority security (only in Frankfurt, not in Madrid). There is an occasional Zurich - Tel Aviv flight on a wide body priced very attractively.
Ever see a sub-1,000 euro long haul business class return? Chances are that it will be with EgyptAir or Saudia. For what it's worth: avoid these carriers at all cost. Not because they're dry airlines (not serving any alcohol), maybe not even because they represent horrific regimes, but because they tend to live up to their - awful - reputation. And even if they don't, you really don't want to transfer in either Cairo, Riyadh or Jeddah.