I have read Lloyd Clark and Rik Atkinison and Clark is a lot better IMHO. Despite it's flaws Atkinsions 'An Army at Dawn' had some merits but I don't think much of the follow up 'The day of battle' it is nowhere near as well written; it doesn't really cover 'The Allies' anyway as it is specifically about the US Army and it has several errors in it.

Also Atkinson is extremely anti-Montgomery and pretty anti-British/Canadian too and he seems unable to mask that when he writes with the result that he belittles the Commonwealth, talks up the US and leaves you wondering if any of what he has written is actually true.

You could also try Cassino by Ellis; I have not read this but I hear it is worth a go and is on my 'eventually' list or tug of war by Graham and Bidwell which I have read and is certainly entertaining.

Er, there is an Imperial War museum book by Michael Carver (could be the same as Richards offering above) called something like a contribution to Victory 1943-45 which is supposed to be OK.

Personally I don't think the book 'by which all others will be judged' has been written for Italy yet and look forward to when it turns up.