First, most people benefit from visual aids: magnifying glasses, binoculars, microscopes (dissecting microscopes in particular) and cameras. Digital cameras are incredibly useful in learning about nature, even the simplest point-and-shoot ones.
Magnifying glasses, especially for children, are a wonderful tool. Most of us have trouble seeing tiny things clearly--the glass allows butterfly eggs, tiny insects, leaf venation, the details of lichen on a rock, all to become easily visible. Plastic magnifying glasses (inexpensive) are good enough for most field trips.
Binoculars bring the distant near--and thus more visible. Children often have trouble with binoculars and their adjustment, but older children and adults usually find them easy to use. The kind of binocular you'll want depends a lot on what your favorite targets are: for butterflies and dragonflies you'll want to be sure the binoculars are "near-focus" but for most birds you don't need that capability. People argue endlessly about binoculars--if you're not already using them, relatively inexpensive (under $150) ones can teach you what you can and can't do, and what you like and don't like about the ones you have...and later you can get the "perfect" ones for you. Do pay for quality glass, more than absolute magnification: a smaller crisp image is better than a larger blurred image.
Microscopes. A school-level dissecting microscope is a really cool thing to have around (put a little pond water or algae in a glass dish and wow!) and will let you define flower parts much more easily in small flowers.
Cameras. The hands-down best tool for documenting what you've seen and helping with identification. If you have a digital image of something, you don't have to lug all your field guides out to the field, or try to remember if that bird had an eyestripe that was straight or kinked, or if the bird with the eyestripe also had wingbars, or the bird with the wingbars was the one without the eyestripe. You can bring the image home, look at it on the computer screen while going through field guides--or you can email it to an expert for help. Beyond the obvious stuff (even a bad picture of a cardinal looks like a cardinal) you need, again, good glass--good lenses--in the camera in order to capture the details that make ID possible. You also need some basic photo-manipulation software so you can crop, resize, and sharpen your images in a non-lossy format (which means your software needs to be able to take the original jpeg the camera handed you and turn it into something non-lossy--and then turn it back to jpeg.
If you're already into photography, you know what you like. If not, start with the simple--a point-and-shoot with the best glass you can afford (ask a camera shop and also try some test shots with it.) You need to be able to see clearly when what you're shooting is in focus (easier with some cameras than others.) Autofocus is fine for some things, but cameras do not understand when what you're after is the detail of the wasp partly behind the flower--so you have to have a way to focus manually as well (or miss a lot of shots.) Some zoom is also very, VERY useful. If you're at the SLR level already, go for the best lens, then reaction speed (how long after you press the shutter does the camera take the shot, and what is the delay in repeated shots?), then at least manual focus option and ideally manual control of aperture and shutter speed, then zoom capability, then pixel depth (megapixels--more is better) then motion-reduction if you don't have very steady hands.
In my opinion, everyone can have access to a magnifying glass. If I had to choose between binoculars and camera for budget reasons, I'd recommend an inexpensive digital camera first....and then inexpensive binoculars before moving to a better camera...the super binocs and the microscope would come later. But if your real interest is in tiny things, the microscope might come earlier in the progression (because an inexpensive camera won't do as good a job at tiny things--can't focus really close), and if your main interest is birdwatching, then good binoculars first and then a good camera. (Incidentally, my dream lens for nature photography including birds is a $7000 lens. Costs a lot more than the rest of my camera equipment put together and explains why I don't have it. What I've got instead isn't as spiffy, but I can take plenty good enough pictures with it, and since I'm not a nationally known bird photographer...so what?)
For some of my bird pictures, here's my "birds" gallery on LJ: http://pics.livejournal.com/e_moon60/gallery/00009084
Not all were taken with the same lens setup or at the same distance--some are "grab" shots where I had just one chance to catch that bird--but they were good enough for ID.