I'm making a character that is going to take the dragon disciple prestige class, and it gives a chart of dragons (White, blue, green, black, red, brass, bronze, gold, copper, and silver.), then says more verities of dragon disciples are available. What other dragons can a dragon disciple choose from?
I've been unable to find any official updates for the class (having looked through Dragon Magic, Draconomicon, and Races of the Dragon in addition to online sources), but I think you can make a few inferences from its design to find suitable additional dragons.
The class fluff references 'dragons' at several points. Presumably, they refer to 'True Dragons' in this line, as most creatures with the dragon type are referred to by their full name instead of simply as dragons, or as 'lesser dragons' more generally. The class also makes references to dragons taking on humanoid form and having children with humanoids, and only the True Dragons have that ability. The list in the class covers every 'True Dragon' in the 3.5e Monster Manual (the only 3.5e monster source available when the disciple was pbulished), and excludes every creature with the dragon type that is not also a True Dragon. While not a hard ruling that the class's options are supposed to be limited to True Dragons, it certainly looks like that's the intent.
Given that, any variety of True Dragon would be a potential option for the class.
The Draconomicon lists the following references as sources of additional True Dragons:
While the Draconomicon defines True Dragons in a somewhat unfortunate and confusing manner, its list seems reasonably acceptable. The list of dragons suitable to create half-dragons in Races of the Dragon (pg 70) seems similarly acceptable and contains some information that would assist with the conversion. Information on how these sources come to their conclusions about what constitues a True Dragon and what does not can be found in the referenced "what is a true dragon" issue.
Note that some of these dragons may have a breath weapon that does not conform to the standard energy damage pattern seen in the prestige class. This may make converting to the dragon disciple's form difficult or inappropriate for certain games and play styles.
In addition to @tarkisflux answer, the draconomicon (page 166 & 167) provides a table of dragons that a half-dragon can be (all of which are specified as being true dragons). Though dragon disciples are not mentioned, dragon disciples are given the half-dragon template at level 10, implying that dragon disciples would have to choose from the same table.