I’m an experienced amateur photographer, but am a total novice in darkroom technology.
If all I want to make are contact prints from full-size negatives, do I need to waste my money on an enlarger? Is there any other kind of controlled light source I can use? Or is there a dedicated device used for contact prints?
No, as long as the illumination is even enough you should have no problem. I assume you are shooting B&W. As long as the spectrum isn’t completely bizarre you’ll do okay. Trying to print contact sheets by exposing with a darkroom safelight might be an exercise in futility 
Since you did say you were a darkroom novice a safelight is a dim light with a filter that only passes a spectrum that B&W printing paper is not particularly sensitive to. It still has to be extremely dim. You can get safelight bulbs and various types of filters as well as complete safelight units. There are some panachromatic papers made for printing B&W from color negs which are fully sensitive and of course all film and color printing materials can only be handled in total darkness.
Get a darkroom timer so you can make consistent exposures. IMO getting an enlarger isn’t a waste if you aren’t going digital and there are astonishingly good buys as many folks are going digital. An enlarger with a diffusion or collimator light source will certainly give the most even exposure.
Just out of curiosity, what format are you shooting?
Control and repeatability are the two factors you need to consider for the light source. You do not need an enlarger, but it sure does make it easy to contact print when you have the abilty to control exposure by more than just time. Which even the cheapest enlarger/lens set up allows.
You can contact print using a desk lamp, but the results will probably not be repeatable nor adequately controlled. Also, some contact papers are designed to work best with specific wavelengths of light.
Searching photographic sites for dedicated contact printers should give you some hits. Back in the 70s there were several manufacturors marketing simple, plastic, all in one units. If I can find one of those, I’ll post a link to it.
Here are some ideas from eBay:
Ancient
You get the idea.
DISCLAIMER: I am not in any way affiliated with either seller. All I did was a search.
Guess I should have explained exactly what I need to do.
I’ve got some 11x17 grayscale Photoshop images, and I want to make traditional photographic prints of them. I plan to print high-res film negatives on my printer, then make contact prints from the negs. So obviously I need a controlled, predictable light source that can evenly illuminate an 11x17 area.
Obviously, I could make smaller negatives and use an enlarger, but I’m afraid that would compromise the quality of the image.
If you are able to black-out the room, an ordinary ceiling mounted room light can be ideal. As noted above even illumination is key so the bigger the separation the better. Ideally an exposure time ~30 seconds makes it easy to time consistently without getting too bored. You will also need some way to keep the film and paper in intimate contact over the whole image. You can purchase a contact frame (expensive for the size you need) or use a thick sheet of glass (~5mm)
Printing usable negatives on an inkjet printer may be a little more difficult than you imagine, but take comfort that you are not alone - the Alternative Photo community (mostly people using artistic, 19th century printing methods) is, ironically, very active in using digital negs for contact printing.
Firstly the output may need considerable adjustment in Photoshop to match with the characteristics of your photo-paper. Not doing so will result in disappointing results which are either too flat (i.e. all grays with no full blacks or whites) or too contrasty with no detail in highlight and/or shadow areas. An excellent book on the subject is Dan Burkholder’s Making Digital Negatives for Contact Printing. This has become a standard text in Alt.Photo.
The second problem is your choice of film to print on. The vast majority of OHP films designed for inkjet printing cannot accept enough ink to give enough density for good results. The current darling of the Alt.Photo crowd is Pictorico film which has a special absorbent layer. When printing you set the paper quality to premium photo paper rather than OHP film so the printer lays down more ink. You can also get excellent results using paper negatives - just make sure your paper has no printing on the back or watermark and that you place the printed side in contact with your photo-paper (beware - the image is then reversed). Your exposure times will obviously go up substantially.
Printing small negs on an inkjet and using in an enlarger can be fun, giving VERY BIG GRAIN, but probably not what you are after 99% of the time.
Have fun
You can use a lightbulb. I used to use a 15 Watt bulb, plugged into a timer. I played with the distances and times until it came out right. You could use an enlarger too, if you wanted to. I switched to an enlarger for the repeatability and better control. There are dedicated contact printers, but some of them are far too bright. If you use the Photoshop method, you will have to play with the curves until you are satisfied. The transparencies and inks you use will also make a difference. Experiment with it. Dan Burkhalter’s book is pretty much the authoritative How To Do It. It would be a good idea, if you can get one, to have a good 8x10 negative to compare to, so you have a feel of how your transparencies should look. Another fun thing to try, is print your negative onto paper, then put that face down on another paper, as the final contact print. Again, you will have to tweak your curves.
Those of saying to use an enlarger are not saying to enlarge your negs. What we’re saying is that using it as the light source for the contact printing yields predictable, repeatable results. It’s still contact printing. The neg never goes in the enlarger, it stays in contact with the printing paper. (Hence the name contact printing.) The enlarger is simply the light source. The other options (like what I linked to on eBay) will also do a very good job.
Remember, you want repeatability and for that you need control. None of the ways listed here so far are wrong, though. So, pick and choose, then experiment.
That sounds like an awful lot of work with little benefit. I could understand if you were making contact prints from large format negatives as you can get some astonishing results and with an enlarger you have potentially much more control.
Since you have a digital original why don’t you just go to some place like Costco? The Maritsu printer at my local store can print up to 12x18. Once you get things dialed in with some smaller proofs you get very repeatable results.
I make my prints from large format film. The enlarger is simply a light source that I can control better than a lightbulb, when I make my contact prints. For me, it is easier and gives better results than the digital megatives I’ve tried so far. But, not everyone has a 4x5, a 5x7 and an 8x10 camera.