For a collection
First, I think you have a good start. My approach to colelcting was to get what appealed to me, and if I decided I didn't like it later, I traded/sold it (sorry cheapshooter).
IMHO, these are guns that are good collection pieces, in that they are semi-common now, but will probably be worth holding onto for a while:
Mosin-Nagant- 91/30; m44; m38, etc- these are in almost every gun shop, but if you look at all the mosin threads on here, you hear people belly-aching about how they won't buy one for less than $80 out the door- their prices have been creeping up, and will probably continue to do so for a while.
Smith Combat magnum- Your model 19 is a good start. Still common enough to get at a decent price, but they should start drying up before too long.
Webley-Scott revolver- classic break action revolver, not too hard to find, as long as you aren't looking for ammo.
Browning HiPower- classic handgun, and if you can get one for a good price, I don't think you'll be disappointed (not from my own experience, since I am still looking for my future BHP).
Certain 1911's- I am no pro on 1911's, but if you can find an older one in decent condition from a good manufacturer, it wouldn't hurt.
These are just based on my minimal knowledge and my own nascent collecting look-arounds. Your results may vary-