On many bikes originally set up for 27" wheels, you can convert down to 700c just by using a 47-57 reach caliper with the pads set down near the bottom of the range. This used to be called normal reach but today is called long reach. Much better to just measure to remove the ambiguity.

If the frame has studs for cantilevers, you may or may not be able to convert to 700c. If the studs are too high for the new, lower rim height, you might be inviting the brake pads to dive under the rim due to the increased angle. Also, some cantis allow for more or less verticle adjustment.

If you need to stick with 27", it is hard to know which current 27" rim to suggest. If you are commuting or touring, the Sun CR-18s and Velocity Twin Hollow both have good reputations (but I've not used either).

Hope this helps.