Yes...er, No... er, what?
This feat has sparked debate for several years. The core of the matter is the definition of "...specifies a single target..."
There are those that rule that this is a requirement that there be a 'Target: one [something]' line in the spell's description, and those that contend that any spell that has a range greater than touch and can affect only a single target qualifies.
With the traps on p.42, the Dungeon Master's Guide II (2005), supports the argument that ray spells qualify. Some of these traps use spells named "X" enervation:
Enervation/Energy Drain Traps
\begin{array}
\ \text{CR} & \text{Spell} & \text{No. of Rays} & \text{Negative Levels} & \text{Caster Level} \\
\hline
... \\
7 & \text{empowered } enervation & 1 & 1\text{d}4+1/2 & \text{11th} \\
9 & \text{chained } enervation\text{*} & 1 & \text{1d4 (primary), 1d2 (secondary)} & \text{15th}\\
...
\end{array}
*While this version of the trap fires only a single ray, the
primary ray branches out from the first target, striking all
other creatures within 30 feet of the first. These secondary
targets, if struck, gain only half as many negative levels as
the primary target.
Chained Enervation Trap: CR 9; magical device;
proximity trigger (target within 60 ft.); automatic reset;
spell effect (enervation, 15th-level wizard, Atk +14 ranged
touch, 1d4 negative levels at fi rst target, Atk +14 ranged
touch, 1d2 negative levels at every creature within 30 ft.
of first target)...
The use of both Empower Spell and Chain Spell, while not using the word metamagic, is strongly implied, due to the spell naming convention and even italicization. This would seem to have settled the issue.
Then, three years later, after the release of 4th edition, the Main D&D 3.5 FAQ, produced this entry in the very last, June 30, 2008, revision (p39):
Can you use the Chain Spell metamagic feat on a spell
with the ray effect type?
To use the Chain Spell metamagic feat, the spell you are
applying it to must have a target entry in its spell description.
Most rays do not have a target entry and cannot have the feat
applied to them.
(Note the 'Most rays'...)
The timing of this edit to the FAQ, enmeshed with the 4th edition release, had some folks at the time either scratching their heads or gnashing their teeth.
The FAQ is a debated issue in itself, even here on RPG.se, with all answers there appearing to say that the FAQ is suggestions and houserules. Of them all, only mxyzplk's answer seems favorable to the FAQ...
What's the answer?
Unfortunately, neither the FAQ nor the DMG II are primary sources for the Chain Spell feat, nor do they purport to be errata for it.
Both rulings have merit, and it must be up to the DM to decide what's better for the game.
Personally, I favor the permissive usage evidenced in the DMG II; so most ray spells could qualify for the feat.