Most tack trunks fall under one of the following categories:
Vinyl Trunks - These are usually the most stylish option, often made with custom colours and the rider's name or initials printed on the trunk. They are available in a variety of sizes and the largest ones can generally fit anything that you'd like to put in there. The downsides to this option are their space requirements and their weight. The larger models can be very wide and therefore don't fit in the more narrow tent aisles. In such a case, you would be forced to put the trunk outside or in a tack stall (it will take up a lot of space in there!). They can be difficult to carry around even for two people, so they are not a good option if you'll be doing most of the loading or unloading yourself. They are also very expensive.
Wooden Trunks - These also look very classy when they are done well. Again, they can come in a variety of sizes but I have found there to be a lot more narrower widths available than in the vinyl category, which makes fitting them in tent aisles much easier. They can be quite heavy, so again, usually two people are required to move them around. The cost varies depending on the size and quality. If you can build one yourself, it can be a very inexpensive option.
Plastic Trunks - These provide a lighter alternative to the vinyl or wooden trunks while still providing some bigger sizes to fit all of your equipment. They tend not to look all that nice and a lot of riders will use a special trunk cover to improve the look. They are generally a bit cheaper than wooden trunks. The Stanley brand is very popular.
Rubbermaids - This is my tack box of choice! They are inexpensive, very light and come in a variety of sizes. They tend not to look all that attractive, but they are practical. One strong person can often lift even the larger ones without help, so they are great if you will be working solo. I also like being able to empty some of them into the tack stall and then just tossing them back into the trailer for storage. Not necessarily the best choice if you're worried about looks.
Whichever type you choose, make sure that the box will fit through the tack room door of any trailer that you will be using. Some of the wider trunks will not fit through your average trailer tack room door and therefore need to be transported specially!