I have a suggestion for IMCDb, though its probably stupid.

I was thinking the site would be more user friendly if when you searched for a movie that had sequels or prequels, the site would list them a the top of the movie page, so if I wanted to look at the movie’s sequel I could just click on the name.

For example: I search for the first Lethal Weapon, I click on the first film, but while I’m vewing the first Lethal Weapon, the sequels are already listed at the top, so I don’t have to go back to search box and start my search again.

Like I said, its probably a stupid suggestion.

People could always post links to the other films in a series in the comments of the main page.

That's what I did for some movies.
Note that if you search "leathal weapon" you have the four movies that appear there, you can simply open links in a new window/tab rather than directly click on them.