Ben Roethlisberger (No. 7 among quarterbacks). Roethlisberger has only one touchdown total in the Steelers' recent games against the Bills and Ravens, but there's no reason not to start him against an average Bengals pass defense.
Rashard Mendenhall (No. 10 among running backs). A great start this week - the Bengals' run defense is well below average, the Steelers are fairly likely to lead in the second half, and as ESPN points out, Chris Ivory had a huge game against Cincinnati last week. Also, Mendenhall is just one game removed from getting 36 carries against the Bills.
Mike Wallace (No. 9 among wide receivers). Wallace has cooled a little bit in the last two weeks after the end of a hot streak that began in Week 9 against ... the Bengals, but he's still a very clear start. Wallace could pass 1,000 yards receiving with a big game, but if not, that's on the docket sometime in the next few weeks.
Hines Ward (No. 49 among receivers). Ward has taken a big tumble in ESPN's rankings, and probably deservedly so. After a big game against the Bills, Ward looked like he had shaken off a four-game stretch in which he only had 53 yards receiving total, but he disappeared against the Ravens, with only one catch. Ward has had three 100-yard games this year, so we know he still has it in him, but I'd bench him unless he stops vanishing.
Steelers defense (No. 1). The Bengals scored 21 points against the Steelers D in their last meeting, but there's no reason not to go with a top fantasy defense against a below-average offense.
Shaun Suisham (no rankings for kickers). Suisham is now 6-for-6 in field goals as the Steelers' kicker, including 5-for-5 from 40 yards or more. If you already have him, start him.