I *highly* suggest going to the John Hancock building instead of the Sears Tower. JH is by the lake, thus much better view, and it even has a decent restaurant near top floor that you can have dinner at. I always bring my visiting friends to JH. Btw, JH is walking distance from the Penn.

You could also have a dinner/cruise package. There are large cruise ships that pick people up from Navy Pier and serves dinner on board. I have not personally tried it so I can't comment on the experience. Sounds romantic to me though.