Stock is a lot of hard work for very little return. I've been on Alamy a few years now and make the odd sale. As KeithT mentions, you need at least 1,000 images to be making regular sales - and the consensus among Alamy contributors is that should be 10,000!! As for subject matter, well, the world is your lobster. My first sale was off a front door of a run down house! The newspaper ran a feature on how we were having to buy old houses and do them up so a front door with peeling paint fitted the bill.
I've also sold views of National Trust properties, Peacocks and Air-Sea Rescue helicopters so there's scope for pretty much anything.
As Karen says though, you're better off going local. I've kept away from newspapers as I know they're tight and am looking more at specialist local interest magazines - the sort who like a nice landscape as a double-page spread each month. I've even emailed Editors with thumbnails attached saying 'did you know they're doing XYZ' which has resulted in publication/money. To give you an idea of difference in money though - the last Alamy sale netted me less than £20 by the time they'd taken their cut and the last magazine spread was £200!
You could also check out local venues - my dad paints and hangs stuff in his doctor's waiting room - and they sell! There is scope to get stuff in local hotels etc but make sure you're a hard business person - don't do the 'well hang it up for 6 months and give me a fiver if it sells' - sell them the framed print at a decent mark up and let them add their own margin on top (I'm doing this at the moment - well, in the negotiation stages but they should be on walls very soon as they've agreed to buy some).
I think the motto is;
Stock does not rock
