Not many tools for reloading shotshells. You need a shotshell press, a scale to check powder charges, wads, shot, and once fired or new hulls.
MEC reloaders are generally recommended.
http://www.mecreloaders.com/
For casual shooters or hunters you would be pleased with the 600 but better yet would be the MEC Sizemaster unit. You can buy 12, 20, or other gauge die sets for it and change from one gauge to another. It has a collet crimp which sizes the head of the case back to factory size.
If you shoot a lot a progressive press that will load more rounds per hour. You'd have to decide what output you need and buy the press that will load the quantity you shoot.
From MEC you'd also need to buy the charge bars for the press you pick. You need a charge bar for each shot charge you intend to load. 1 1/8 bar for 1 1/8 oz of shot, 1 1/4 charge bar for 1 1/4 oz. loads etc. You also need to know what powder you are going to use and buy powder bushings that will throw the correct charge for your load.
I recommend the shellchecker from MEC that has a go-no go gauge to check the sizing of the heads of the hulls.
You need a good reloading manual or three. Lyman 5th Edition Shotshell manual is great. BPI (Ballistic Products Inc) has some good manuals and components. Hodgdon and other have reloading data on-line.
So, you need a press, shot bars and powder bushings, and a powder scale to get started. Most important thing in loading shotshells is hull identification and using the exact components listed in the manual. Use the exact primer, wad, powder and charge.