[ams6110]

The only things I really know of that would still use vacuum tubes are esoteric high-end audiophile amplifiers, and some "old school" guitar amps (Marshall, Hiwatt, etc). Is there really that big a market? Are they used for anything else?

[stan_rogers]

You are overlooking things like magnetrons, x-ray tubes, photomultipliers, CRTs (which still have a lot of applications outside of the video display sphere), krytons and so forth. It's not all about diodes, triodes, tetrodes and pentodes.

[arctangent]

Wikipedia lists some other modern uses including (most unexpectedly) in particle accelerators:

http://en.wikipedia.org/wiki/Vacuum_tube#Vacuum_tubes_in_the...

[chrischen]

I believe NORAD computers still use vacuum tubes.

[sliverstorm]

One of my professors told me a few years ago that tubes were still used heavily in high-power commercial radio stations. Could be dated info though.