Go to members.aol.com/tjscustom/Web/TJ-list.htm and check out T.J.'s work. I hear that he is "the man" when it comes to Sigs. I have a P220 as well and am considering sending it to him to smooth out the action and lighten the trigger a little bit.
i have carried my 220 quite a bit and there isn't much that it needs but...i had
1. the action tuned by a local smith who has done serveral guns for me www.dmcustomguns.com
2. trigger reduced, rounded and polished
3. sharp leading edge of slide beveled (where it flares out to full width)
4. hogue rubber grips (without front strap)
i'm looking at some possiblities for front strap treatment (conamyds?) and seeing if a heinie rear (i like the straight 8 night sights) can be fitted (w/o looking like an old NM gun)
i've heard good things about TJ custom and also John Q's (works out of his garage somewhere in sacramento ca) but have no personal experience
I find the sights excellent and the pistol EXTREMELY accurate. The trigger is smooth but a little high in effort.
I had an action job done by "Actions By T" www.actionsbyt.com. Mr. Jacobson specializes in action jobs and does superior work. He is brutally frank about the pros and cons of each pistol (I sent him a CZ, which he doesn't like - but he did a wonderful job).
I'd consider sending mine but want to get more rounds through it. Other than getting the grip right, I'm not going to mess with it - it's a TERRIFIC pistol.