Unfortunately, there do not sem to be any tutorials that quite match your intentions, at least none that I know of. Different OS desiginers have different goals and visions, and each one reflects the trade-offs and priorities of the original designer. Also, most of them were not written to be tutorials, and so many are rather confusing to follow. Generally, those tutorials that are out there are either documentation of an existing design added as an afterthought, or else are limited 'demonstration' programs written solely to show one part of the process without really accomplishing much. Ironically, the part most often skipped is the actual loading of and transfer of control to the second stage, which is the most important (and most difficult, despite the complexities of p-mode and file systems) part of a boot loader, by definition. Finally, many have been written rather carelessly, and often the actual 'tutorial' code doesn't not actually work.
Generally, most boot loaders follow one of two directions, which can be called 'file-system first' and 'p-mode first'. These generally reflect whether the design is going from high-level to low-level or vis versa. Some truly butch coders may wish to try to do both, but usually, the space limitations are such that it is not feasible.
The reasoning behind the 'filesystem first' approach is simply that, while it requires a greater code commitement that is often difficult to fit into a bootloader, it allows you to use ordinary executable files as your kernel, rather than a raw binary. This makes it far easier to use the system itself as a development platform, measn that, in your disk, only the boot sector itself is a special case not part of the filesystem. Also, many amateur OS developers want to use an established filesystem - FAT in particular, as it is well known and trivial to implement - which usually means that the sectors following the boot sector (not to mention the DIB in the boot sector itself) are already spoken for by the file systems design. Thus, if you want to use FAT (or ext2fs), you have to read the filesystem to get the second stage for loading.
The 'p-mode first' approach is more common among designers for whom the filesystem is a secondary consideration. The usual goal here is to make the transition from real mode to protected mode either before or during the transition to the second stage, thus ensuring that the system code is all 'p-mode pure', and they can avoid having to worry about having to deal with 16-bit code after that point. While this is in many was a nice idea, it is also means that you often have to set up the GDT and related tables on relatively limited information, usually hardwiring the system assumptions that could be a problem later. Also, it means that the second stage has to be loaded as raw code (unless you've also managed to fit the FS code), which makes the process of recompiling and reloading the kernel more difficult, especially if the size of the kernel changes.
I know it isn't reall what you want, but I would recommend taking a look at my own bootloader example at
http://204.215.248.28/board.jsp?message=1539 (it is also at
http://www.mega-tokyo.com/forum/index.p ... readid=775 , which is probably a bit easier to read). It is the closest thing to what you are talking about that I know of, and while it is sparesly commented right now, I have ben considering rewriting it as a tutorial (with substantial additions to cover some specific circumnstances, and considerably clarified code). ALso, while they are hardly a comprehenisve example, you may want to look through CrazyBuddha's "Baby Steps" pages on Megatokyo
(
http://www.mega-tokyo.com/forum/index.php?board=1). HTH, somewhat at least.
and jump to them.