I use Jumbo Booms from Ambient Recording; in the USA they're www.ambientaudio.com:
From the brochure:
"Jumbo booms can be extended up to 12 meters and use segments up to 40 mm in diameter. While not suitable for hand held use, numerous accessories are available for mounting jumbo booms on Manfrotto stands with a cantilevering angle bracket and counterweight. In this configuration they can be used to place microphones up to 12 meters above ground level for studio, classical music on location, church organ, feature film crowd scenes, etc. Jumbos can also be used to position small cameras, lights, measuring instruments and antenna."
For booming mics into those hard to get to places or even setting up a Decca Tree using three stands from the back of an orchestra they work a treat. I don't know whether I'd trus a Decca Tree of heavy LDCs on one but a pair of something like M149s is fine up to 30' or so.
They're not cheap but they are pretty portable. an comfortable one man lift and they easily fit into a medium sized estate car (e.g. Audi A6). I don't know how important that is for you but for me it's essential.
And for really high work on stuff like pipe organs, I have one of these:
It's a a Clark Teksam S QT 15/HP pump up ariel mast which goes up to 15m (45' or so) with a 2.5kg (5.5lb) head load. Clarks make a huge range of masts for civil and military use covering a wide range of heights and headloads.
I sprayed mine black to make it a little more discrete than the yellow one in the picture. Though with something that big, discrete is a relative concept.
Again, it's not cheap but you can get a carefully balanced Decca Treeof something not too heavy up to about 35-40ft if you really want to; or a pair of Brauner VM1s up to over 45 ft (though you do need to mount the PSUs on the mast if you only have the standard 7.5m cables!).
It folds down small enough to fit into a Subaru Forrester/Audi A6 and is not too difficult for one man to carry.