Where I work engineers who sit at desks seem to wear a long sleeved button up shirt, slacks, and dressy shoes, departments heads tend to wear that as well.
Engineers who get up from their desks to go into the manufacturing area typically wear the plant floor uniform.
The uniform worn on the plant floor is tan or navy blue pants, and either a navy blue polo style shirt or a light blue oxford shirt. They also wear steel toed shoes and a belt that doesn't have a metal buckle.
The IT department is expected to wear the plant floor uniform. I personally prefer the short sleeved oxford and tan pants, since that's what many of the supervisors in the plant wear. My direct supervisor always wears navy blue pants and a long sleeve oxford. Our department manager wears a navy blue polo style shirt that's made of that synthetic material that's supposed to keep you cool and ironed tan cargo pants.
We've got a fairly wide range of engineers though, Mechanical, Design, Industrial and maybe one or two Electrical.