The first thing you should do when you get your slides or negatives back is record some basic information to associate with each of the images. First, sort the slides and discard any slides that are unusable. Next, record the data. At a minimum, you should record the date an place the picture was taken; on slides this can easily be done on the slide mount. I use a rubber date stamp to record the date (working from information in my field notebook); then I use a Rapidograph or Pigma Micron waterproof pen (not that your slides would ever get wet) to record the place the picture was taken. It is easy to stamp or write on cardboard slide mounts, plastic ones are trickier. I found that plastic mounts will take ink OK if I am VERY careful not to get fingerprints on the surface before writing, and if I give them plenty of time to dry. If I know the identity of the subject I will also jot it down at this time, otherwise I so so later on when I identify the subject with the help of a key or field guide.
Writing information out is trickier to do with negatives; you can sometimes write on the sleeves that the negatives come in or you can order special sleeves which will allow you to write information on them. Be careful - since the information is not on the negative things can get mixed up whenever the negatives are out of their sleeves.
With the site information and date recorded, I then sort the slides. There are several ways to store slides; it depends on how much room you have, how much money you have, or how convenient you want access to your slides to be.
In terms of price and minimal storage space, it's hard to beat the plastic slide boxes that come with your slides. You can label them with tape and put similar slides together. Even labeled like this, however, it takes a while to find the slide you want.
Much more convenient, but more demanding of space and money are slide storage pages. These clear plastic pages have room for 20 slides each. Most are punched for 3-ring binders and/or hanging file bars. The big advantage here is that you can organize similar slides on a page, and the pages can likewise be organized into hanging file boxes or 3-ring binders complete with index tabs for easy location. When you pull out a page you can instantly see 20 slides at once - which is a lot faster than going through a box of 20 slides one by one. Similar pages are available for prints and negatives. Be sure that the slide pages you get are PVC free. Some cheap pages are made of PVC vinyl, which gives off gasses which can damage film.
No matter which system you use (I use both, with my "better" images in pages and lesser images or unidentified images in labeled boxes), be sure the pages, boxes, or binders are stored in waterproof containers. It's not like a pipe would break and flood your office and ruin hundreds of slides, but it doesn't hurt to be careful.
Besides water (which would never get to your slides), you need to guard against humidity, which can warp cardboard slide mounts and allow fungus to grow. You also want to avoid extremes of temperature - about 70 degrees F (20 degrees C) is ideal if the humidity is low. If you must store slides in a cool but humid environment (i.e. the basement), be sure that they are in sealed plastic boxes and that each box has a desiccants in it. These desiccants, made of silica, can easily be recharged in an oven.
Finally, light and heat will cause your slides to fade. You can avoid this by not projecting them and by keeping them in dark places. Kodachrome slides are supposed to last about 50 years. I have some of my grandfather's slides which are that old, and some have faded more than others (not all were Kodachrome, though). My own slides, starting from 1980 and mostly in Ektachrome, have held up well for 20 years, even those which are projected a few times a year. Ultimately, though, there is digital archiving, which should never fade.
Storing Images Digitally
Once an image has been scanned into a digital form, theoretically is can be stored forever without any sort of degradation. If it is on magnetic media, it should be recopied every year or so to fresh media; as the magnetic fields fade over time and need to be refreshed. CD's theoretically should last as long as the plastic disk does, but there is a hitch. Mass produced CD's are actually stamped; the CD's your record yourself has the image literally burned into a thin layer on the disk. If this layer can be burned once it is vulnerable to burning again - or just plain aging. So, CD's you make yourself should be redone every 20 years or so.
One problem with digital archiving - even if the media are stable, there is no guarantee that the equipment to read it will be. How many of you have an 8" floppy drive that will read a diskette from an IBM DisplayWriter? Seriously - I have a file I want to download off one. We think that CD's will be around forever, well, that's what a lot of people thought about LP's. Older technology becomes obsolete as newer technology replaces it. DVD is poised to replace CD, at least a DVD reader can read a CD. And even if the media can be read, will software to make sense of it be around?
The only good news about these ongoing technological upheavals is that each successive generation of technology seems to be capable of holding much more than the previous one. For instance, early PC's that I used had 5MB hard drives and 360KB floppies. I had quite a collection of floppies, but when I got a computer with a 30MB hard drive they all fit on it easily. Tape drives could hold 80MB, so I could back up my whole hard drive. Today, hard drives are much bigger, but I can get all of the courseware, email, and web pages I have developed (and I'm talking all my syllabi, class notes, quizzes, tests, grade sheets, etc., including each year's versions) back to 1980 on a CD or two. All of that would fit on one DVD. So, as long as I don't get into recording moving images (which really eats up memory), I should be able to continue to migrate things onto each new medium, have all my old stuff fit, and have room for the new stuff.
In any event, in the year 2000 the only game in town is CD for archiving images. Any magnetic media can be damaged by magnetic fields (or water, as unlikely as that might be). DVD is coming, but is not a cheap as CD is now. You can get over 640MB of images onto a CD which will cost less than $1 when bought in bulk.
To store your files on CD:
Of course you will store the CD carefully, protecting it from scratches. Incidentally, on many recordable CD's the data is written on a layer which is on the underside of the label, so be careful not to scratch the label side.
At this point, if you are paranoid, you will take the last backup CD you made and send it off to someone else in a different city, so if there is a firestorm or a flood your data will still be safe.