Help! Does it exist?
I'm looking for a performance/arranger keyboard to play jazz, blues, rock 'n' roll, modern pops, ballads etc preferably with more than 5 octaves - so I can play bass in the left hand on occasions, and left hand boogie patterns too.
I need one with the facility to put a microphone through it, and it shouldn't be more than about 35 pounds in weight.
Any ideas or does such a keyboard not exist?

if you can give up on the mic input, i could recommed roland e60. if not, i dont know. maybe some newer casio might have it.
if you want to spend more, you have couple of alternatives: g70(maybe too heavy), korg pa1xpro, ketron sd, yamaha 9000pro (little bit old)...

Have you done a search here on the SZ there are many discussions on many KB choices for you.

If you want 76 keys, your choices are slim, indeed. The BIG 3 becomes the Big 2 on this issue....!

If money is no object (or time - it won't be out for quite a while) that new Ketron Audya looks interesting.

If you can compromise about the weight (you may have to, there are only a couple of 76-ers in your stated weight limit) the G70 or PA1XPro are both good (in different ways.

If an older arranger would work for you, a G1000 is a good choice (and the Chord Sequencer is excellent for blowing solos on top of a head you just played).

But my advice would be to forget the weight issue (just get a very light case!) and give the G70 a hard look. Wonderful jazz styles, a killer grand piano sound, a killer key-bed, a killer B3 sound, and killer drums. Most of what you need for a jazz gig......

You don’t give us your price range, but I assume it is in the Tyros 2 range, if so then most Jazz players (At least in the UK) go for the Korg PA1X Pro http://www.korg.co.uk/products/professional_arranger/pa1x_pro/pa_pa1x_pro.asp or Ketron SD1. http://www.bck.co.uk (The Yamaha and Rolands tend to be too staid to really pull off Full Jazz)
If you’re prepared to spend more, then go for an open keyboard like the Wersi Ikarus http://www.harmony-music.co.uk/ikarus.htm or Lionstracs Mediastation, http://www.lionstracs.com/store/ and get yourself the Garritan Jazz VST http://www.garritan.com/jazz.html and also the Native Instruments B4 VST, http://www.native-instruments.com/index.php?id=b4ii_us which will allow you to really get the Jazz beat going.
As to the weight issue, then I am afraid that the larger the keyboard, the stronger the case and support has to be, which of course means extra weight.
Hope this helps

Bill