Thanks all. Some great suggestions. I'm putting a list together.
To answer a few questions: @hivemindneeded The Canning Town branch of Celia Hammonds. For every cat we take in there are probably another 20 that we have been asked to take in but don't have space for. The problem here is huge.
Why no people names? Just because, firstly, they've all been done to death and, secondly, it's easy to find lists of them for inspiration if you want to go down that route. I'm hoping for more original names.
Why can't we use the same names again? We can and do. I just get bored of seeing the same names going round and round. And if, a year or so later, someone contacts us about problems they're having with 'Oreo and Peanut' for example then it makes life so much more complicated as there are so many of them. I'd like the cats I name to be a bit more unusual so that, if it comes up, I know it's something to do with me and can get involved.
Names that are used over and over are: flowers, herbs, spices, trees, planets and all foodstuffs, particularly biscuits and sweets.
And I don't want anything in foreign languages or which isn't an easily recognised and easily repeated word as that causes problems when people are trying to remember the names of cats they've seen on the website to enquire about them.
And I can't really have anything too out there. If I named my next ones Potency and Impetus @FelicityBeedle people would think we had lost the plot entirely 
. Although I am still really tempted by Broccoli Highkicks .....
As I said I'm going to make a list and expect to see them on a website near you soon