Well, you're sort of limited for choice in the UK. I found that the way Apocalypse is 'half' buried underground allowed me to get on the ride and get strapped in etc, without really realising how high it is. Having said that, I think it was Hurukan Condor that was my first 'real' drop tower!
I found that it was the anticipation that killed me with drop towers, however after riding a few on the USA Live I've become a lot happier riding them. They still get the adrenaline pumping, but I'm not going to 'wimp' out anymore.
Just go for it! They can be intimating, but just think "if these people in line can ride it". You'll love it once you're off it.