We have some artwork available to print your own decals for your model projects:
One of the things that always hindered me in the past in choosing a particular aircraft to model was the lack of appropriate decals. Sure, there are a lot of after-market decal sheets available, but since I always want to have some photographs of the actual (individual) aircraft that I am modeling, finding both photographs and decals for the same aircraft is often very difficult. Mostly, this is an issue of serial numbers, tail numbers, and other such details that identify the individual aircraft; national emblems, squadron markings, etc. you can typically find from those after-market decal sheets.
A few years ago I started experimenting with making my own decals, using decal paper, a graphics program on my computer, and a good printer. The process is simple:
The first phase is probably the most difficult, and usually the most time-consuming. I tend to use "Adobe Illustrator" on my Mac to do the graphics, but any reasonably capable graphics program will do. This article is not intended as a tutorial on how to use a graphics program; my experience is that the most capable programs (such as Illustrator) require some practice before you become proficient and can produce the result you desire.
If it is just a question of tail numbers, and you have the appropriate font available, you could even use a text editor (for example, there is a font available called "AmarilloUSAF", it gives you the USAF lettering). For my own favorite topic, the Finnish Air Force,  has a picture with all the different letters and digits for standard wartime tail numbers. I scanned the picture, and "extracted" each individual letter/digit into a separate image file. I can use these images to assemble any Finnish Air Force tail number very quickly, and then scale it to whichever size I need (I use Illustrator for the assembly). Similar reference sources exist for other air forces as well, e.g.  has information about Luftwaffe lettering. If you scan images, make sure the resulting files have sufficiently high resolution to print properly.
Next, how to print the decals. Several options exist, first you have a choice between a laser printer and an inkjet printer, and then whether to print on white or clear decal paper. Notice that most printers (certainly all laser and inkjet printers) cannot print white ink, since white is usually just a "hole" in the graphic. When you print on clear decal film, there is no white, since whatever color your model is (where the decal gets applied) will show through. I have been able to achieve a good result by either applying a separate white decal underneath my own decal, or painting the area white first before applying my decal. A company called ALPS used to make dye-sublimation printers which were capable of also printing white, but I don't think these are available anymore.
If you only need black lettering/graphics, you can print on photo paper using an inkjet, and then photocopy on decal paper intended for laser printers, since copiers effectively use the same technology as laser printers. Inkjet printout may sometimes bleed when the decal is applied and gets wet. In any case, the printed decals have to be coated before application. When I used the Microscale "Liquid Decal Film" I had some minor bleeding of colors, but after I switched to the Krylon Acrylic "Crystal Clear" coating (in a spray can), I have not had any issues. Krylon now allows me to print directly on the decal paper using my inkjet printer. I have only used "Experts-Choice" decal paper from Bare-Metal Foil Co., but other choices exist as well.
I try to format my decals in such a way that I can print on the top edge of the decal paper sheet. I then slice off the decal using a paper cutter, and the remaining sheet can be printed on again (decal paper tends to be pricey). Also note that printing on white decal paper means that your decal will eventually have to be trimmed very carefully; with clear decal paper you don't necessarily have to be quite as precise. Regardless, what you end up after printing and coating is one big decal with all the graphics attached, so some trimming and cutting is called for.
The resulting decals can be applied normally. I have had good results using MicroSol as the setting solution to get my decals to properly conform to the contours of the model.