I think Argos will be safe - for a while anyway; they've just posted good profits for the last quarter. Eventually I can see them become more an online store with collection points out of towns.
WHSmiths is the one I fear for next, I get all my stationary from the one in the Arndale in Manchester and it's like a ghost town most of the time.
HMV were just badly managed IMO; they needed more focus on what they were best at - music - and not trying to sell MP3 players and headphones which have smaller margains anyway. If they'd stuck to their core business AND got into downloading/streaming in 2007 they'd be in rude health.