Sorting is such an important skill and in my opinion one of the easier things to introduced so I got N (23 months) started with these Sesame Street pictures (cut apart from an old bulletin board border I had).
We use the tray that the Melissa and Doug Magnetic Letters came in (you can use any type of tray, bowls, plates, etc.). I put one picture on each side to get her started telling her "Elmo goes over here and Cookie Monster goes on this side.". She took over from there and loved it.
Other Sorting Ideas:
Poker Chips (sort by color)
Pasta (sort by type: Penne/Macaroni)
Two Different Letters Cut from the Sunday Ads (ex: 5 letter Bs and 5 Letter As)
Pieces of Straws (sort by color or sort by size: long/short)
Pom Poms (sort by color)
Legos (sort by color)
Food from the Play Kitchen (sort by color)