Which camera you should buy will be solely dependent upon what you want to do with it and, of course, your budget.
Most people who answer your question will automatically think of 35mm format SLRs, which is perfectly fine. But considering how incredibly cheap used film cameras are today, why not skip 35mm format and just dive into the deep end of the pool and get a medium format camera? Take a look a at a Yashicamat, Mamiya C330, Rolleicord or the highly coveted Rolleiflex.
Medium format cameras use a much large film, which produce much sharper images, which much higher contrast and tonality. They are much slower to use than a 35mm format SLR, so they will force you to slow down, take your time and think about what you're doing. Since you're a beginner, this is a good thing. As a result, you end up taking fewer, but better images. But, of course, the camera has to be designed for what you want to photograph. So if fast action is part of what you like to shoot, a medium format camera is not for you. Medium format cameras are amazing for anything moving very slowly or not at all. No 35mm format camera can touch the look of medium format.
Medium format cameras often look very intimidating to the beginner. But the way you use a 35mm SLR or a medium format camera is pretty much the same. You focus, meter, compose and then take the shot.
If you think 35mm is right for you, here's a list of auto-focusing 35mm format camera bodies to consider:
Canon: Elan, Elan 7, A2, EOS-3, and EOS-1 (or some variation such as EOS-1v). All of these were top sellers when new, and are designed very well.
Nikon: N6006, N8008, N90, F100, F5 - All of these auto-focusing SLRs were among Nikon's most popular when new. All of the Nikon "N" models have "S" versions. For example, the N90 was later replaced by the N90s. The "S" designation mainly meant that it was a faster (s for speed) camera with improved AF. Remember, auto focus was first introduced in 1985, so even 10-15 years later, the manufacturers were still making improvements in the speed and accuracy of their AF systems.
Avoid the Nikon N4004 and N4004s like the plague as it was Nikon's worst and one the least reliable SLRs they have ever produced.
If you would prefer to use a manual-focusing SLR, then consider these models:
Canon's last manual focusing models used a good deal of digital tech. If you want a manual-focusing SLR but with some modern tech, consider the Canon T series of cameras:
Canon T-90 which was Canon's best (and arguably THE best manual-focusing SLR ever made by anyone) SLR used by professionals for many years. It was Canon's last SLR to use the FD mount, which was replaced by the EF mount that's used in today's cameras. You can get lens converter to use old FD mount lenses on cameras today, but they are very awkward to use and typically not worth it. So if you go with an old Canon body, just consider that your lenses are not very good on newer DSLRs.
Canon T-70 - My first SLR was a T-70. Unlike the Nikon models at the time, the T-70 was among the first SLRs to have a digital readout in the viewfinder showing the exposure and other very useful information. Other brands were still using the match-needle also called the stick-and-needle way of metering. This method had a needle (control by the camera's metering system) and a arm with a hoop at the end. The idea was that when the hoop was centered over the needle, you then had a good exposure. The user moved the hoop up or down by adjusting the aperture or shutter speed. The T-70's system was much more accurate and is now used in all DSLRs today.
I would skip the Canon T-50 which was auto everything only. You could not control the exposure.
I would also avoid the Canon T-80 which was Canon's first attempt at auto focusing. It's considered the worst SLR in Canon's history.
If you want Old School manual focus, consider these Canon bodies:
Canon FTb was an old manual SLR. It's one of the very few Canon SLRs to have mirror lock up. ML is highly coveted feature for macro shooters. It allows the user to move the mirror to it's up position prior to taking the shot. This reduces the amount of camera movement caused by the mirror slapping the top of the mirror box, resulting in sharper images. A very sturdy and reliable camera; in all my years working in a camera shop, I never once saw one come in for repairs.
Canon AE-1 and AE-1 Program - The main difference between these two models was that the AE-1 Program was fully automatic, thus the "program" in its name. The most popular SLR ever made, it's an icon among camera enthusiasts. It was designed for the beginner photographer. Its very, very reliable.
Canon A1 - An upgrade to the AE-1/AE-1 Program. It was designed for the intermediate photographer who wanted more features such as the ability to use a motor drive. It's very similar to the iconic AE-1. The A1 improves on the AE-1 by allowing for a motor drive vs just a auto advance bar on AE-1 bodies, and it has a wider range of shutter speeds than the AE-1. The difference is that the auto-winder on AE-1 bodies advances 1 fps, while a motor drive on the A1 shoots 5 fps which was the fastest that you could get at the time. The A1 also had a few more shooting/exposure modes.
NIKON manual focus SLRs - Almost anything from Nikon was a good camera. The FE, FE2, FM, FM2, F3 (their pro model costing $1,800 new) were all great cameras. STAY AWAY from the Nikon EM which was their worst manual-focusing SLR.