The pic above is an eldar vehicle from epic, which sort of matches the description the rumor gives for the eldar flyer.
Please remember that these are rumors, and as such always require a little salt.
via Stickmonkey
I expect releases for tau, eldar, dark eldar before end of August.
Based on what I've heard/seen
Eldar are getting a dual kit. A fighter, bomber/heavy attack, and transport were in the works. The heavy attack craft and transport most share a design aesthetic. So this is what I am expecting.
The closest design analog I can give as a hint for the new eldar flyers is the wedge shape Jedi star fighters in the Star wars prequels.
Tau are getting a fighter/gunship in a single kit. Roughly the size of a Stormtalon. Has new missile options. Not the existing tau seekers.
Rule wise ( remember Im not good at getting accurate rule info, so add your own salt and keep it off the forum please) its supposed to take advantage of markerlights in a different way...allowing for indirect fire on any target in range with a markerlights on it from any other tau unit. This is with all it's weaponry, not just missiles. Or so the rumor goes.
Tau have a transport flyer also which should be out with the codex, not before.
Dark eldar should finally see their bomber.
And the most interesting bit, which some may have already had a hint of, there is a third Necron flyer, it uses one of the sprues from the new scythe kit...but don't hold your breath for it...I don't expect it until 2013-...ish....