Several riding web sites have a section devoted to explaining how to do certain tricks. These are all flatland-related I guess a "dump truck" needs more explanation than a "no-footed jump". But trick names are often meaningless: a trash compactor, ashtray, and cross-footed swivel are all the same trick, depending on who you ask; same goes for gerator/gyrator/lard yard, and blender/Circle K/(John) Donut.
Although spending too much energy trying to memorize trick names is a waste of time (learning them is more important), those riders who are just starting out will find these sites pretty useful. All of the sites listed below list trick names and do their best to describe how they're done, but it's not as effective as actually showing the trick. Some sites illustrate the trick with a photo; others go the extra mile and include QuickTime movies so you can actually see how the trick is done. Pictures and video definitely help a lot, especially when the descriptions are confusing and/or wrong.
Below are several sites that can help you learn to ride flatland; the one thing you'll need to work out on your own is patience...
BMX Trix
This site is probably the most useful, since it offers pretty accurate trick descriptions along with a lot of QuickTime movies. The only negative thing I can say about it is that the trick list page isn't divided into skill levels. Other than that minor flaw, this is one of the best how-to pages I was able to find.
Bobby's BMX Freestyle World
Horribly ugly site design here, but that's not what we're talking about. The flatland instruction page is broken down into four skill levels, from "no skills" up to "Jedi Master". There are only a handful of how-to's, but the descriptions are fairly accurate (though written in a BMX Plus style) and all are accompanied by QuickTime movies.
Flat School
Brought to you by Flavor `zine. No video or sequences here just trick descriptions, although many include a photo (which is better than just words). Tricks are broken down by skill level basic, intermediate, expert, pro and there are a pretty good amount of them, but the descriptions are a little on the short side.
Geoff's BMX/Freestyle Land
This was the only site I found that included non-flatland how-to's. Although a few of the tricks listed include a link to a photo, almost all are just descriptions. Tricks are broken up into sections dirt jumping, street/ramps, and flatland and given difficulty ratings (a nice touch), but I would argue whether some of these are actually "tricks" (a turn-bar dirt jump is kind of a stretch) and some are kind of incorrect (a cross up is not an X-up). The how-to descriptions are pretty short and peppered with spelling errors.
The Flatlander
Only a few tricks here, not listed by skill level, and no accompanying photos or video. Descriptions are kind of confusing (even when you know the trick they're trying to describe), and there are some mistakes/inaccuracies (yes, there is a difference between a regular and forward Karl kruzer).
Howjadodat Not Freestylin's interactive freestyle how-to's: a message board where riders can ask for help on how to do a trick, and get advice from riders. Can't figure out how to do something? Try asking someone here.