Airgas.... but they were ridiculously expensive for a 5lb tank.. also they don't fill they swap, they have a bunch of locations though so they are convinient.
Nobby Bev in Plainville, CT does refills, not sure of price yet; but now that I have a 20lb aluminum tank that is pretty I'll be going there so I can keep my pretty tank :-)
Primary: "Not a Chardonnay" white
Secondary: Cabernet Franc, Malbec
On Tap: Blonde, Brown, Cider, Marzen
Bottles: King Czar Stout, Wee Heavy Scotch Ale, Christmas Lager, 2 buck chuck wine
Aging: RIP RIP Stout (Rest In Peace Russian Imperial Stout)
Next batch(es): Cider