I'm thinking my Glock 17 needs a friend.  He might get lonely as the only handgun in the safe.  I've got some .45 brass saved and I also have a little bit of .38 Special brass.  That means his new friend has to be in one of those two calibers.  I think I've narrowed it down to three possible companions, a S&W Model 19 in 4" pinned and recessed, a Glock 21, or a Sig P220, most likely a cop trade in.  Looking on Gunbroker, they're all three gonna cost pretty close together, so that isn't a real decider.  Right now, I'm slightly leaning toward the Model 19.  They haven't made any for a while and those old Smiths are starting to get collectable.  It's also a revolver and everybody needs one of those.  A very close second is the P220.  The G21 is last because a Glock is pretty much a Glock.  My hands are big meat hooks so the grip size on the G21 isn't really a problem, but the Sig definately looks like some nice iron.  They all three are gonna be range pieces mostly.  I might carry the Sig when I get outta Illinois though.  Considering what I want out of it, which does the hive mind think I outta go for first?  Thanks.  

get the one that you can get right now for the best price i'd guess

the smith, like you surmised might be the better bet for now, esp if they are getting a little tougher to find...

overall, nothing wrong w. any of your choices imo

Yes, a revolver is something all gun enthusiasts should have in their collection.  

I'd go with the P220 due to the fact that it will handle hard cast bullets - mine loves 200 grain round nosed flat points from Oregon Trail.

Can't go wrong with a revovler if you don't have one yet.

For a final choice, you may consider the XD45 - standard or tactical length depending on your preference.  13+1 rounds and these too will shoot economical hard cast bullets.  Further, with a democrapic win this coming year, high capacity types will most likey be targeted for a new ban, so you may as well get one now - someting to consider anyway - ditto for the Glock too of course.

I'd skip on the P-220. If I was gonna buy a single stack .45, I'd get a 1911.

Get the Model 19, IMO.    

Get thee a revolver. A classic Smith is always a good choice, but if I were buying a NEW revolver, I'd probably go Ruger.

Ilove my G-19, the XD 45 is an excellent .45 i have the compact tactical and it shoots extremely well

Revolver.  Decision made.

I like the P220 way better than then Glock 21.

Don't forget....FNP-45 is coming out soon as well. If it is anything like other caliber models, it will be a great gun for the price.
I always recommend HK USP, but it does cost a lot more. I am saving up to purchase the newly released HK45. Do not buy a Glock...I find the ones I own really boring now. I am going to keep G34 for IDPA, but getting rid of G19 as I would use my USPc as concealed if I carry.

1) Model 19
2) Sig Sauer 220
3) Glock 21

Looks like you have your *to buy list* worked out.

I'd get a second G17 or a G19.

Only then would I buy a pair of 45's.

Two is one.