Many web sites (including Hasbro's) state that early Monopoly games didn't include tokens. While Charles Darrow didn't include tokens in his sets, Parker Brothers has from the beginning.
The first Parker set had six metal tokens: iron, cannon, thimble, ship, shoe, and top hat. These are listed on the patent issued 12/31/35. The Deluxe #9 edition had these 6 tokens plus the lantern, rocking horse, car, and purse.
It is said that Darrow got the idea for these tokens from children playing the game using charms as tokens. Folkopoly has stated in his book "Passing Go" that he discovered the origin of the tokens through an interview with Mary Utterback (one of the children in Darrow's neighborhood). She said the children bought charms from Kresge's, a local store, and used these as tokens. Darrow was so taken by this that he wanted to include these in his games, but was unable to find a supplier. The idea for tokens went with the sale to Parker Brothers, into the Parker games, and onto the Darrow patent.
Wooden and composite tokens were substituted in some sets as metal ones ran short in 1935. In 1936 a "junior" set was released that had seven wooden tokens as standard (this set remained in production until 1956). Cylindrical tokens were used in some #6 sets in 1936, but these seem to be rare substitutions (smaller cylindrical tokens were also used in some 1942 #6 blue box sets, but these seem to be extremely rare). The picture to the right shows the 1936 tokens on the right and the 1942 tokens on the left.
The 1936 standard set added the car token to bring it's total to seven. The #8 popular edition added the purse as well to bring it's total to eight tokens. The 1936 "New Edition" had seven tokens including the purse, iron, ship, top hat, car, shoe, and cannon. In 1937 the purse was removed and replaced with the thimble.
These tokens remained in place until WW2. The metal shortage brought the return of the composite tokens. No one is sure exactly what these are made of, but they were very crude (this is probably why they were dropped in favor of metal in 1935).
After the war Parker wanted to go back to metal tokens, but Dowst/Tootsietoy had dropped metal tokens in favor of plastic, so Parker Bros. decided to manufacture the tokens themselves. However, it appears they could not get all the same dies as the original tokens so the tokens they began producing were: car with driver, shoe, top hat, thimble, long cannon, ship, and iron (for the sets with seven) the dog completed the #8 popular edition, and the horse and rider, and the wheelbarrow completed the deluxe #9 (some of the #9s dropped the shoe and added an airplane token).
By the mid 1950s the car had been replaced by the more familiar race car (it had a 3 on it until sometime in the 1960s), so all the tokens resembled today's tokens. Over time Parker Bros. again farmed out the production of the tokens, different dies were used, but the basic design has remained the same for the past 50 years.
In the 1960s the #9 became the standard set and was dropped to eight tokens (race car, top hat, thimble, shoe, ship, Scottie dog, iron, and long cannon).
By the early 1970s the tokens were changed to: race car (no 3), horse and rider, wheelbarrow, thimble, top hat, iron, shoe, and dog. The 1975 40th anniversary edition added back the ship and long cannon to have ten tokens.
By the 1980s the #9 again had all ten tokens. In 1985 the Deluxe anniversary edition (50th) was released with a new token (train) available only in the deluxe edition. In 1998/1999 an eleventh token was added to the standard #9 (money bag) bringing the total to eleven in the standard editon and twelve in the deluxe edition.
Other tokens were used over the years as well. Early pricey editions had larger tokens, and most recently the 1997 Heirloom Edition had a piggybank token added. The 1985 Commemorative Edition had reproductions of the original ten in antique brass, and the Franklin Mint edition had these same ten tokens but plated in 24 karat gold.
A chart listing all sets that use standard tokens can be found here. This chart does not contain the larger tokens used in the Fine, De Luxe and 60th anniversary sets.
The specialty editions all have their own tokens relating to the theme (over 1100 at last count) so I have not even attempted to go into those.