The Smith-Morra Gambit (1. e4 c5 2. d4 cxd4 3. c3) is popular at club levels, and is played at least occasionally by even some masters. If Black accepts the gambit by taking the pawn on c3, White will play 4. Nxc3, gaining an early initiative and a dangerous attack.
While this gambit may not be entirely sound, it is dangerous in the hands of a player who knows the opening well, especially against an unprepared opponent.