The number of Electoral College votes for each state is determined by their number of members of Congress. Thus, smaller states have slightly disproportionate influence in the EC, as states with only one House of Representatives member (Alaska, for example) have their vote tally tripled by the addition of votes for their two Senators, while large states, like California with 52 House members, receive a much smaller incremental benefit for adding their two senators to the count.
By tradition, most states' electors distribute their votes on a winner-takes-all basis, as mblase wrote. However, Maine's and Nebraska's electors allocate their votes differently. The two votes notionally representing each state's senators are given to the winner. Then, the remaining votes are allocated based on the popular vote winner in each Congressional district of the state in question (currently 2 in Maine, and 3 in Nebraska) -- effectively, a miniature version of the national Electoral College based on the Congressional district map. Barack Obama was the first presidential candidate to win an electoral vote this way, claiming the elector representing the second Congressional district of Nebraska (mostly Omaha and its suburbs) in 2008 despite John McCain's statewide triumph.