The Huffington Post has this column by Rob Richie, advocating bigger U.S. House of Representatives districts that would each elect three (or possibly more) members. Also, the column advocates the rules used for the Illinois House of Representatives 1870-1980, in which parties are free to decide whether to run one, two, or three nominees in districts like this. Then, voters would be permitted to use cumulative voting. A voter could give all three of his or her votes to a single candidate, or give one vote to each of three candidates, or give one-and-one-half votes to each of two candidates.
This may sound complicated, but it would not require a constitutional amendment. Nor would it require changes to vote-counting machines. But t would require Congress to repeal the 1967 law that requires all states to use single-member districts for U.S. House. Thanks to Rick Hasen for the link.