There's no such thing as a wheat head penny. There are wheat back cents with a bust (head and shoulders) of Lincoln on the front.
You can find values at the following sites:
http://www.numismedia.com/fmv/prices/lnccnt/pricesgd.shtml
http://www.numismedia.com/fmv/prices/lnccntmo/pricesgd.shtml
Two pennies that were minted (made) before wheat pennies were Flying Eagle cents (1856 - 1858) and Indian Head cents (1859 - 1909).
Because Indian Head pennies are older than the more familiar wheat and memorial cents. Thus, less are preserved and they are scarcer. Also, many times the mintage figures were much, much, lower on early Indian Head pennies than on even wheat pennies, let alone memorial cents.
There were no Indian Head pennies minted in 1915. The last Indian Head pennies were minted in 1909. In 1915 the type of penny minted was the Lincoln, Wheat Ear reverse (called 'Wheat penny'). A 1915 Wheat penny is worth from $1.50 to $500.00 according to mint mark and condition.
Wheat pennies were not made until 1909. In 1900 the pennies were Indian Head Cents. A 1900 Indian Head cent would be worth about $1 in Good condition (good condition is the fourth worst condition possible).
The wheat design was used on pennies. This coin is normally called a Barber or Liberty Head dime.
The first wheat pennies were dated 1909 so you must have an Indian Head cent. See the Related Question for more details.
Wheat pennies from 1943 are zinc-coated steel, not silver. On average, they're worth 10 cents.
The only penny being produced by the US Mint in 1885 was the Indian Head penny. Wheat pennies were not produced until 1909.
Wheat pennies were only made from 1909 till 1958. See the related question below for the value of a 1890 Indian head penny.
The last year Indian Head pennies were minted was 1909. In 1927 the type of penny that was minted was the Lincoln, Wheat Ears reverse (called 'Wheat Penny') A 1927 Wheat penny is worth from $0.15 to $125.00 according to mint mark and condition.
Wheat pennies were made for the first time in 1909, with a date of 1901 the coin is a Indian Head cent and average value is 50 cents to $2.00 for circulated coins.
The 1964 Lincoln penny is unfortuantely worth 1 penny. This was not a key date amongst pennies. Most valuable pennies were wheat and Indian head cents dating from 1859-1958