I love Daddy has probably my favorite big dick conversation. And it does get quite the reaction.
The Olivia Route on Big Brother, as well as your Aunt Kira, and one scene regarding the little sister... but I'd by no means call this a good game.
Dating my Daughter also has numerous big dick reactions... though again not what I'd call a good game.
Parental Love might have them, but I don't recall them as well, so not sure.
There is one or two in Dreams of Desire iirc... but again, I'm not entirely sure.
Often times, as writing quality goes up, gags like the "Oh my god its so big" gag disappear in favour of good storytelling. It still sneaks its way into some games, but I wouldn't count on those games that do it always being good. That said, its prevalent enough that you should find it in most things you'll play, we have a trope thread and both big dicked protagonists and girls hypnotized by the dick get mentioned.