I've stayed many a night in the City Inn, it is a nice hotel, as is the Crowne Plaza across the river.
They are a bit out of the way though, no tube that close, walkable into town of course but not exactly in the middle of the action.
If you can stretch to it the Marriott County Hall is nice, there's a couple of new hotels nearby (Park Plaza I think, not stayed there)
The Guoman (used to be Thistle) at Charing Cross is the best placed though, couple of stops south of Euston on the Northern Line, right at the top of Villiers St so you can finish the night drinking port in Gordon's wine bar, which is where my wife and I stayed last year for a weekend restaurant/theatre trip