If you're looking for information on ITF Taekwon-Do obviously you should invest in Gen. Choi's encyclopedia. There is a condensed version of about 750 pp. that you can pick up for a little over $100. If you're interetsed in greated depth get the full 15 volume set. Both are available through TKD Times.
As for DVD's and other multimedia training aids you can check out Com-Do's Legacy CD-Rom set. It contains 4 discs which include a scanned version of the 15 vol. encyclopedia, a Korean translation section by Master Choi, Jung Hwa and all 24 patterns demonstrated from multiple angles. The patterns are performed quite well, although there's no instructional commentary with them. You can pick these disks up at www.comdo.com
The best product I have seen in the DVD category is Mater Choi's Master Class DVD. It covers the first 9 color belt patterns from various angles and includes commentary and instruction on common problem areas from Master Choi himself. An excellent product which can be found at www.trenic.com
There is also a 2 disk DVD set put out by the Japanese ITF group under the NK's that covers up to 3rd dan patterns. One of the performers is Hwang Su Il, he of Hwaorang fame from the video game Tekken. Available through TKD Times.
I agree with chrisspillertkd - if you are looking specifically for ITF information, the items he lists are considered the standard reference sources for the Ch'ang H'on (ITF) tul set and their applications. I would invest in one or more of those before buying something else that's not on his list - not because other references are poorly done (although some are - not the ones on this page, but others) but because those are the ones that most, if not all, ITF practitioners use as reference points, while many of the others, regardless of quality, do not necessarily emphasize techniques the same way - not good, not bad, not right or wrong - just differently, and that could lead to confusion.