"Gees Whiz" is a popular expression often used to express surprise or amazement. There are a variety of synonyms that can be used to convey the same emotion. Some of the possible synonyms include "wow," "amazing," "incredible," "unbelievable," "fantastic," "awe-inspiring," "mind-blowing," "astounding," "remarkable," and "phenomenal." Depending on the context and the level of intensity needed, other options may include "holy cow," "oh my goodness," "golly," "whoa," or "holy moly." When seeking to express enthusiastic approval or excitement, any of these synonyms can add some zing and excitement to your conversation.