Are there any sites that have walkthroughs for non ero VNs, like say if I wanted to play through the PSP release of Killer Queen, Code Geass Lost Colors, or any other games like that?
Either use Eroge RSS Checker, or search for the game’s title + ??. Just like with eroges, there’s no single site that has a kouryaku for every game.
Another thing I like to do is to type in one of the choices (exactly, so use the same composition style and doublecheck) and put that and the game name in your search query. It tends to work a good portion of the time when the other methods don’t.
A damn shame too. You’d think Japan would adopt something like GameFAQ’s. According to a 2chan thread I read a loooooong time ago, several of the (then) most active walkthru sites discussed about merging, but things prevented them from coming to an agreement.
Oh, I forgot to mention one other useful tool. The ??? tag on EGS can be helpful for suggesting the best clear order for eroges that could be spoiled or otherwise weakened if cleared in the wrong order. Generally most good walkthrough sites, such as Foolmaker will have the endings arranged in the best order, but it can be helpful if you want additional opinions.