The most important part of your knife is the blade; therefore, you want to be very careful about what sort of knife you purchase. Materials for blanks vary from the basic stainless steel to venerable Damascus steel to the newest alloys, and all of them have advantages and disadvantages. You also have to consider your knife's eventual size so you'll know how big a knife to purchase. Before purchasing, know what you're getting.
Stainless steel is the most basic you can get, and it's good for general purpose knives. The stainless steel variety won't hold as good a blade as many of the other alloys, but they look nice and are good for general purpose use. Stainless steel knife blanks are the least expensive available that actually make decent blades.
Talonite is made of a cobalt-chromium alloy that forms carbides, so it tests soft by most hardness tests even though it's very hard and wears extremely well. If you try to cut a Talonite knife with a band saw, you will wreck the saw, so you'll need an abrasive cut off wheel instead. Ceramic belts do an excellent job of grinding Talonite, but other types of belts don't do so well. Carbide drill bits will be necessary for drilling holes into Talonite.
Closely related to Talonite is Stellite. Knife blanks made of stellite resist corrosion and wear. Stellite doesn't oxidize easily in any condition, and resist heat well. Both Talonite and stellite are more difficult to work with than stainless steel, so are better for an experienced knife maker. Before buying either material, consider the equipment you have to work with. Though stellite and Talonite blanks are of temptingly good quality, if you break your drill and band saw while working with them, it's not really worth it.
Titanium knife blanks are very good for knifemaking; in fact, the highest grade of titanium is called knife-grade titanium. Titanium is an
alloy of iron, oxygen, carbon, and various other materials; titanium benefits from the strength of the material, but it is a little brittle compared to other materials. Titanium takes a good blade as well as a good surface finish.
Damascus steel isn't the Damascus steel of the Crusades, but rather a modern reproduction. When you look at a knife of Damascus steel, you'll see patterning on the metal; this is the carbides in the metal, which precipitate out during forging and strengthen the edge far beyond the capability of iron alone. Damascus steel blanks today are generally pattern welded steel, which is made of layers of steel and iron which are welded together; Japanese katana are made this way. If you get a made of Damascus steel, don't expect it to be just like the old blades.
A nifty new twist on Damascus steel is Timascus, which is a titanium Damascus; Timascus is limited in availability, and should be treated the same way as titanium. These will closely resemble steel Damascus, and vary widely in color due to the particular alloy used. Knife blanks of this material will hold a highly polished finish, which will be brightly colored; or you can give these blades a pearly finish, which will show off the ripples in the metal nicely.
You may find other materials, but these are the basics. Before purchasing, do some research on the materials; there are different grades of each, especially stainless steel, and while some grades make excellent knives, others make excellent butterknives.
Before buying a knife blank, make sure you have your new blade planned, and have considered the size of the resultant knife while you're looking for suitable material. You can't glue extra metal onto a knife blade, nor can you be certain of cutting of metal if it's too large. It is probably best, in fact, to know the size of your handle before shelling out the cash.
Good planning, careful consideration, and a mind for the artistry of your eventual blade will all help you choose the proper metal for your purposes. The knife is the most important component of your knife; if the raw goods are bad it doesn't matter how good the rest looks. Consider your options carefully before purchasing. Seriously.