You're going to have to compromise with the optical drive if you want a small case.
Slimline optical is pretty much it for m-itx cases with a "set-top box feel"
Couple of suggestions I'd make within your budget are Antec ISK 300 (comes with either a 65w psu for a touch under £60 or a 150w psu for a touch over £60)
Coolermaster Elite 100,comes with a 150w psu for around £45.
CIT and Jou-Jye also make a lot of cases in this style so google those also.
I've built a couple of Htpc's now with AMD's E-350 (Zacate) boards,I'd take one of these over an Atom setup any day of the week,the gpu acceleration is far superior to anything Atom based.