Alignment as written: Easy and simple, works for most games. The problem being when you get classes like paladins, where certain actions break the unbelievably strict code: What, exactly, is lawful? Especially when military actions are concerned. Are Paladins allowed to use guerilla warfare? Would they not be paralyzed if the enemy took but a single hostage?
My favorite system is almost as simple, fits within the rules, and makes more sense from a flavor standpoint- In my games, patron diety=alignment. Detect evil scans for followers of gods that are listed as "evil" in the handbook (it's an FR campaign), and thus considered "evil" by whoever designed the detect evil spell. For a class with an alignment restriction, only the gods listed under those alignments offer training for that class at their temples and in their cities. That way, all of the gods can have their own "versions" of the same alignment. If player characters want to switch alignment, it's as simple as visiting the local temple of your new god and being initiated into their following.
That seems to work in my more talk/character/plot heavy campaigns, but that may be because I have a group that likes to nitpick the alignment system. I used the normal alignment system for years and didn't have any problems until I started running stuff for my current group, the kind of group that has members who love to browse the PHB when it's not their turn in combat so they can torment me with all the inconsistencies and unrealistic traditions of the fantasy genre.
Still, alignment is one of those things that isn't a big deal until you make it one, so I usually find myself agreeing with the posts at the top of the page...
-Willowhaunt