Mesh riding jacket.

[PhilBiker]

Look for a mesh jacket with ballistic cordura or leather in the key crash zones; back, elbows, shoulders.  I've got a mesh jacket and pants from Marsee (who no longer makes riding clothes) which has CE armor and heavy cordura at key locations.  Fits great and is really cool in the hot weather.

[FiremanBob]

I wear a Tourmaster Flex which is a great compromise. Good from 40s to 70s.  The fact that the outer arms and shoulders are not mesh makes it still too warm on the hottest summer days.  

For this summer I'll be buying the Vanson "mesh shirt", a minimalist jacket with full armor and a cordura mesh outer that is much tougher than the polyester mesh in most other jackets.  Under $200. It's the best hot-weather mesh jacket I've seen.

[county]

Joe rocket "Santa Fe"  combo of perf leather and mesh.  (And armour)

[Clive]

I have the Joe Rocket Reactor 2.0: mesh body with perforated leather over the shoulders and elbows.  No leather down the back, but I have my Speedmaster (T-Pro Forcefield) back protector on when I'm riding.

The jacket flows air well and has a sportier cut.  The liner also worked well in cooler temps.  There's only the 8" zipper to join it to pants, though -- no circumferential zipper.

[btcooksr]

I have a used, Joe Rocket Reactor Mesh for sale, all black with liner, XXL. Make an offer.

[Troubl]

Newenough.com has a good deal on the Teknic Supervents right now...

http://www.newenough.com/closeouts/mesh_jackets_and_pants/teknic/supervent_mesh_motorcycle_jacket.html

[scrmpyjack]

I Have a New REV'IT mesh style jack.

I have had a couple of JR and Tourmaster mesh jackets.

And this jacket (Rev'it) is buy far the most confortable and Best looking.
As for the armor, the Rev'it has the Knox turtle type (standard).  
It is more substantial than just the foam type that comes with the JR or tourmaster, unless you upgrade it on your own.

The included back pad is your standard foam type. I took it out and wear my SPIDI Warrior all the time.

I rode 1100 miles in two days and it was in the 90s I felt just as comfortable as I did wearing any other fully meshed jacket.
Except that the Revit is not 100% mesh. There are non-perferated material inlays over some of the arm and shoulder area were the armor is underneith.  I feel that it would be less likely to snagg in a get off and keep the armor in place better.

The Revit gear is more form fitted.  It looks neat like a good jacket should.

Besides I grew tired of wearing way to many tacky brand patches on what ever I am wearing.

I am looking at the NEW Revit riding suit.  I never liked the stich

[rauchman]

Just picked up a Tourmaster Draft mesh jacket at my local shop.  Works very nicely.  Haven't crash tested it (and hope not too).  I like it much better than the Cortech GS Sport textile jacket I picked up last season.  The GS (maybe it's GX) felt like slipping into a plastic garbage bag.  Never liked the feel of the jacket.  The Draft fits better too.