The most popular number by far is 7, considered lucky by many people. Another hit is 17 due to its central position on the table. Also, 8 is lucky in many Asian cultures and will also be frequently bet on. As for the unlucky numbers, you'll rarely see people betting on 13 for obvious reasons.
Some bets in American Roulette have an even higher house edge than the 5.26% average. For example, a bet on the Five Numbers (0, 00, 1, 2, 3) carries a house edge of 7.89%. Outside bets in roulette carry the lowest risk. They cover more numbers yet the payouts are lower (1/1 for Red, Black, Odd, Even, 1 18, 19 36).