The Fridge Brilliance that sets in after Bowler Hat Guy reveals that Cornelius Robinson, this brilliant, successful, world-famous inventor/industrialist/patriarch of the amazing and loving Robinson family, is Lewis' future self. You realize: Oh my, this is Lewis' future if he doesn't give up, and what's even better, he builds it himself.Anvilicious as it is, it works.
Cornelius showing Lewis around his lab and pointing out his favorite invention, the same one Lewis entered in the science fair and which won him his new family. Tom Selleck nails it to the wall.
The final scene with Wilbur. He finally fills his end of the bargain and takes Lewis to see his mother from the night she left him in the orphanage, even if it means that he'll be risking his existence again.
Wilbur: I never knew my dad could be my best friend.
Also, Lewis' response to Wilbur's question, "Why did you just let her go?"
Lewis: Because...I already have a family.
The fact that Wilbur, despite likely knowing how much of a risk it posed (and probably being utterly terrified of what would happen if it went wrong), kept his promise. Flawed he may be but Wilbur is a great kid.
Wilbur watching Lewis present the Memory Scanner at the science fair. He actually saw his father show off his greatest invention for himself. The proud smile on his face says it all.
Lewis saying goodbye to the Robinsons... for now.
The ending quote, revealing the origin of the Arc Words.
Around here, however, we don't look backwards for very long. We keep moving forward, opening up new doors and doing new things, because we're curious... and curiosity keeps leading us down new paths. — Walt Disney
The Robinson Family. They aren't just pure awesome... they're pure heartwarming.
One particularly touching moment is when Lewis' attempt at fixing the peanut butter and jelly device results in it exploding. Lewis is plainly terrified that the family will be upset (like the couple earlier in the film) and starts to stammer out apologies frantically. To his obvious surprise, they start congratulating him on a wonderful failure (well, except Petunia) and Billie passes on the excellent aesop of "From failure, you learn. From success...not so much."
During his second attempt to use the Memory Scanner, Lewis asks his volunteer, who later turns out to be Grandma Lucille, for a memory to input. She goes through several possibilities, including winning a medal for the luge, and then finally selects one...her wedding day with Grandpa Bud.
The fact that, as he knows it works, Cornelius encourages his future wife to be the crazy singing frog lady despite people thinking she's probably mad...
A minor one, but when the Bowler Hat Guy ponders how to lure Lewis out of the Robinson house, he at first contemplates blowing it up, but he rejects this idea, seemingly not having the heart to kill Lewis.
Lewis hugging Mildred goodbye. It's clear his Parental Substitute still means a lot to him. And then he leans out of the window as he, Lucille and Bud are driving away and waves goodbye to her.
A fanfic crossover with Big Hero 6 reveals the possible fates of Lewis and Goob. Lewis, who is now known as Cornelius, is indeed a successful inventor with a great family. Goob, on the other hand, has become the world's most elite baseball player, thanking Cornelius for his success. However, it becomes a tearjerker because everyone from the Robinsons, along with Goob, have died of old age.