1. A computer-based method for use by a trader in an electronic trading system that includes at least one computer terminal connected over a network to at least one electronic exchange, the method comprising: receiving by a computing device a command to buy or sell a spread, wherein the spread is associated with a first real market and a second real market, and wherein the first and second real markets are offered by at least one electronic exchange; determining by the computing device a plurality of spread markets that offer interchangeable tradeable objects, wherein a first spread market of the plurality of spread markets is a synthetic spread market that is generated outside of an electronic exchange and associated with the first real market and the second real market, and wherein a second spread market of the plurality of spread markets is an exchange-provided spread market that is also associated with the first real market and the second real market; determining by the computing device a first price for which the spread can be bought or sold in the first spread market and a second price for which the spread can be bought or sold in the second spread market; in response to receiving the command, determining by the computing device whether to buy or sell in the first spread market, buy or sell in the second spread market, or buy or sell in both the first and second spread markets based on the determined first price and the determined second price, and responsively: sending by the computing device a first spread market order for at least one of the first and second real markets when it is determined to buy or sell in the first spread market, sending by the computing device a second spread market order for the exchange-provided spread market when it is determined to buy or sell in the second spread market, or sending by the computing device the first spread market order for at least one of the first and second real markets and sending by the computing device the second spread market order to the exchange-provided spread market when it is determined to buy or sell in both the first and second spread markets.