Other dock species of the Rumex genus: (from Billy)
Rumex patientia - Patience Dock, Herb Patience, Spinach Dock, Passion's Dock
Rumex orbiculatus - Water Dock, Great Water Dock
Rumex obtusifolius - Broad-leaf Dock, Bitter Dock

Description:
Coarse leaves with wavy margins stemming off from obvious joints on the strong, ribbed stalk.  Dense heads of small, greenish flowers which become seed heads that change to a reddish or brownish color as they mature emanate from the top of the axils where the leaf joins the stem.  Seed husks are marked by their heart shaped wings.

Statistics:  (from Audie)
Height: 2-4 feet (60-120 cm)
Leaves: 6-10 inches (15-25 cm) long, oblong to lanceolate, crisped margins
Flowers: 1/6 of an inch (4 mm) long, sepals in 2 cycles of 3, petals absent
Fruit: seed-like, brown, enclosed by calyx of 3 "wings" with smooth margins
Roots: yellowish taproot
Season of flowering: June-September

Habitat: (from Billy)
This perennial can be found from early spring (as a basal rosette) through late summer (when the stalks reach heights of up to 5 feet) in open fields, vacant lots, gardens, roadsides and other waste places. R. orbiculatus can be found in swampy areas and around lakes, ponds, rivers and streams.

Uses: (from Brillie)
Basal leaves used in salad when young and steamed or cooked as greens in early spring.  Mid-spring flower stalks can be stripped and used as a vegetable raw or cooked.  Roots have a variety of medicinal uses.

Nutrition information: (from edibleplants.com)
Curly Dock (R. crispus):  calories 21, protein 1.5 g, fat 0.3 g, calcium 74 mg, phosphorus 56 mg, iron 5.6 mg, sodium 0 mg, potassium 0 mg, vitamin A 1,385 (I.U.), thiamin 0.06 mg, riboflavin 0.08 mg, niacin 0.4 mg, vitamin C 30 mg
Dock (Rumex spp.):  calories 28, protein 2.1 g, fat 0.3 g, calcium 66 mg, phosphorus 41 mg, iron 1.6 mg, sodium 5 mg, potassium 338 mg, vitamin A 12,900 (I.U.), thiamin 0.09 mg, riboflavin 0.22 mg, niacin 0.5 mg, vitamin C 119 mg

Lore: (from Brillie unless otherwise noted)
Crispus means "curly" in Latin.  The common name "yellow dock" derives from the long, stout, yellow taproot.  "Dock" is the word for the solid part of an animal's tail, and "to dock" means to remove the tail, as is done to sheep and dogs.  All weeds were eventually called "dock" in English, perhaps because people tried to remove, or "dock" them.  Dock is not related to burdock which is in the artichoke family.  It is, however, (per Billy) related to the sorrels which are also of the genus Rumex and the Buckwheat family Polygonaceae. 

Comments: (from Brillie unless otherwise noted)
The basal leaves have a unique sour flavor and are good in salad when they are young (wash them first--the chrysophanic acid in the leaves can irritate your mouth.)  They are also good steamed or cooked as greens, having 33% more protein, iron, calcium, potassium, beta carotene & phosphorus than spinach and 50% more vitamin C. 
When the leaves start to turn bitter in mid spring, the flower stalks can be cut and peeled to add to salads.  They can also be cooked (one minute of parboiling makes them soft.) 
A decoction of the root, high in potassium, manganese and iron, is good for treating anemia, and it is not irritating to the gastrointestinal tract as iron pills can be.  It is generally considered a good blood purifier.  The root decoction is also a liver decongestant that stimulates bile production.  Due to concentrations of anthraquinones, it is a safe laxative good for relieving constipation (Meddie).  However, it can likewise be used to stop diarrhea as well because of it's tannin content (Meddie).  Tannin also makes dock root an astringent that can be used to stop bleeding and to help skin irritations.
One of the best known uses of dock is for curing nettle stings.  Rub the leaves of curly dock on the burning area.  Brillie reports that the British say, "Nettles in, dock out."

Bibliography:
Audie 709w,  Billy 49,  Brillie 236,  Eddie 154,  Meddie 214

Curly Dock
Rumex crispus
(Billy 49)