Everyone will have their own ideas about this, but I'll take a shot at answering...RecreationalBoom wrote: If you had no collection but had a few grand to use to start one, what would you buy?
Since you have a center fire pistol, I would suggest the following to round out or begin your collection...
1. .22 rifle of your choice (semi auto, bolt...doesn't really matter, just get one you like)
2. .22 pistol (ruger, browning buckmark, or whatever floats your boat)
3. A decent center rifle rifle in .30-06 (whatever action floats your boat)
4. 12 ga. pump shotgun (or semi auto).
These along with your XDm pretty much covers all the bases from concealed carry, paper punching, small game, wing shooting, sporting clays, or taking any big game on the North American continent. Everything else is just gravy. Pass the gravy please!