Although numbers stations are less common than they were, there are at least two groups which follow/catalogue/categorise their continuing activity.
Extremely dedicated groups have the following websites:
http://priyom.org/
http://www.apul64.dsl.pipex.com/enigma2000/
and
http://www.simonmason.karoo.net/page30.html
Remember that there are Morse and data numbers stations too. But possibly more intriguing are the related odd noise stations operating 24/7:
'The Buzzer' 4625 kHz audible across Europe from dusk
'The Pip' 5448 kHz (daytime), 3756 kHz (night time)
'The Squeaky Wheel' 3828 kHz (night time), 5473 kHz (daytime)
Then there's the 'backward music' or 'whale song' station that appears from time to time.
Most of these stations are clearly audible after dusk in the UK. They seem to be from the Russian military, and the noises are just used as channel markers with voice messages being fairly rare.
Googling numbers stations will bring up more pages, but for anyone wishing to follow this subject up, priyom.org (mostly UK-based volunteers) is a good place to start, with audio samples and a clear frequency list.
I find some of these signals fascinatingly creepy - especially when listening in the shack, alone... at night...
Ian