Well I use poundhost and am happy with them, reccomended
I don't use anyone in redbus / telehouse but these are very good datacentre's by reputation. Work has many servers in a redbus cage, you could look into this possibility, If you need to colo 8 atx cases in a data centre who charge by the U then it's going to cost you a lot, as you will need at least 1 rack probably 2.
I would reccomend talking to Tim Anker at the Colocation exchange (http://www.colo-x.com/
) Very helpful and can probably find you something for you needs.