Long-billed Dowitcher, Limnodromus scolopaceus
Long-billed Dowitcher, breeding plumage, 5/7/06, Edwards NWR, Alviso
The bird above, from Spring 2006, shows all the marks for Long-billed -- no substantial white area on the belly, no primary extension, the diagnostic barring on the side of the breast, and the characteristic pattern in the scapulars and coverts. Though I didn't hear it call, the identification seems clear.
Long-billed Dowitcher, breeding plumage, 4/30/05, Palo Alto Baylands
The two birds on the left,  photographed in Spring 2005, both gave the single sharp "keek!" call that is diagnostic of Long-billed Dowitcher. Short-bills call a soft mellow "tu-tu-tu." In addition the two bird have good visual field marks for Long-billed. The top bird of the two, which still retains a few winter feathers as it completes its molt to breeding plumage,  shows no substantial areas of solid white on the belly, more sharply marked contrast (black and white rather than rufous and buff) in the mantle and scapular feathers, and the primaries don't extend beyond the tertials or the tip of the tail. The lower bird shows the primary pattern of LB, and the ground color of the barred tail feather is rufous rather than white, also a mark for LB.
Long-billed Dowitcher, breeding plumage, 5/2/05, Palo Alto Baylands
Long-billed Dowitcher, 8/31/05, Edwards NWR, Alviso
The two birds on the left, both seen in fall still mostly in breeding plumage, both have the all-red underparts characteristic of Long-billed. Most of their dark marks are worn off; Short-billed usually retain more of these markings. And most of the retained marks on the side of the breast are bars rather than spots. There doesn't look to be any primary extension, though in both cases molt confuses the issue. The lower bird has more plain gray upperparts feathers molted in. In neither case did I hear the bird call, so the i.d. not entirely certain in either case.

Below, another "probable LB" from Spring 2006, molt confusing the primary extension issue. Tail shows LB pattern, black bands broader than white ones, and all-red underparts (albeit faded.)
Long-billed Dowitcher, molting, 9/3/05, Palo Alto Baylands
Long-billed Dowitcher,  7/23/06, Edwards NWR, Alviso
The two below, from Fall 2007, show white on the belly; this is an SB mark, but not a reliable one, once molt is underway. These both show faint residual barring on the side of the breast, a mark said to be diagnostic of LB, and no primary extension.
Long-billed Dowitcher, 8/4/07, Edwards NWR, Alviso
Long-billed Dowitcher, 8/2/07, Palo Alto Baylands
Dowitcher species (Long-billed?), 8/28/04, Shoreline Park, Mountain View
The bird on the left has mostly molted to winter plumage, and I didn't hear it call, so it must be left "Dowitcher species." But I include it on this page as there are several indicators of Long-billed: it's foraging along the banks of a fresh-water stream; it has barring rather than spotting on the side of the breast; the tail barring fits LB rather than SB; the posture is humpbacked rather than flatbacked; and no primary extension is visible. In most Short-bills the dark primary tips, barely visible in profile here between the tertials and the tail, project beyond, creating a dark spot at the rear of the bird, as here.
Long-billed Dowitcher, juvenile, 10/14/07, Radio Road, Redwood Shores, San Mateo Co
Juvenile plumage, fresh with scapulars darker than adult non-breeding plumage, and narrow light fringes on the tertials; no internal markings on scapulars, as found on juvenile Short-billed.
Long-billed Dowitchers, flying, 8/25/08, Radio Road, Redwood Shores, San Mateo Co
Flying dowitchers in migration season, some still mostly in breeding plumage, some mostly molted. The breeding plumage birds show the all-rufous underparts characteristic of Long-billed.