The basic no frills gun is the Remington 870 Express Magnum HD model. This has a synthetic stock, black powder-coat finish, bead sight, and synthetic trigger group. This is an excellent HD gun right out of the box with no mods.
The only minus's, are, that to add a magazine extension, you have to remove two tabs of metal from inside the magazine tube. This isn't too tough a job. Second, it now comes with Remington's PC lockable safety, that everyone hates.
Top of the line is the Remington 870 Magnum Police model. These come in walnut or synthetic stocks, parkerized finish, aluminum trigger group, yes or no on magazine extensions, and a good choice of different sights. They also have heavy duty mag springs and shell releases. They do not have the PC safety.
The Express is a inexpensive entry level HD gun that can be upgraded, while the Police models are rather expensive but top-of-the-line. If you want to save money and do it yourself, I'd go with the Express HD, as long as you don't want different sights or finish.
If you want a gun that's complete out of the box, I'd order whichever model of Police gun that met my needs. To see the Police model lineup go to:
www.remingtonle.com
The third option is to buy a used 870 and add the options and finish you want a peice at a time.
I've done the do it yourself route and usually wind up spending about what a new Police gun costs. Partly because I added rifle sights, and had refinishes done.
Last time I just cut to the chase, and bought a Remington Police model already set up like I wanted.