ExpertFlyer is offering a 20% discount to new subscribers through July 15, discount taken off of the first monthly or yearly bill (so the savings are much greater on an annual subscription) with coupon code PKYGEZFT. The discount also works for gift certificates.
There are basically two pay services that advanced flyers use. Expert Flyer is one, and is of especially good use for American Airlines flyers looking to upgrade internationally, and for Delta upgrades, for instance and because the site will keep searching for inventory to open up on routes you designate and ping you when it does.
Personally I use the KVS Tool. It lacks award availability for Swiss (which is a drawback for me, but I workaround the problem via the Lufthansa JetFriends program) and it lacks the ExpertFlyer feature of automatically checking for specific inventory on your behalf and emailing you when it becomes available. But it has a broader variety of tools and access to special inventory of more airlines. I find it particular useful in putting together award itineraries, as it provides efficient access to the All Nippon Airways search engine for Star Alliance awards (giving you pretty much everything but Swiss and Air China, the latter of which can be searched for using the KVS Tool’s Apollo access), Oneworld awards via the Qantas and Cathay Pacific award search engines, and Skyteam awards via the Northwest US and Japan sites.
ExpertFlyer works off of a direct computer reservation feed, while KVS tool screen scrapes from various websites, providing convenient access to a wide variety of information.
If you do consider an Expert Flyer subscription, you’ll probably want to take advantage of their free 5 day trial first before committing, especially as the discount is valid far enough into the future that if you sign up in early July you can do the trial and then at the end take advantage of the discount if you do find the tool valuable.