In Pres. Bush’s past “State of the Union” addresses, he used to give us a pep talk about the UK’s role in Iraq along with other allies. Is Blair still in the game? Do we still have allies interested in Iraq? Haven’t heard too much about this, lately. (And, if the allies are there, haven’t their numbers dwindled?)
Bonus Q: Isn’t Blair as unpopular in the UK as Bush is in the US?
He’s more irrelevant than unpopular. He resigned over six months ago.
Related question - is there any head of state who cooperated with Bush to invade Iraq, and still holds power?
Who’s in and who’s out in the military sense.
Yeah, I actually thought this was common knowledge.
Queen Elizabeth II
Except he’s angling to be President of Europe. 
Doesn’t count - Her Majesty had no personal involvement in the decision, and simply acted on the advice of her government. If you take your approach, she’s simultaneously in the ranks of heads of state who did not cooperate with Bush - as Queen of Canada, she took the advice of her Canadian government, which did not send troops.