The rules say you can cast spells as an in-grapple maneuver (subject to some strict limitations), but don't appear to expressly mention spell-like abilities. Yet in most ways spell-like abilities act and cast as spells without components. Does being in a grapple preclude the use of spell-like abilities?
Yes you can use them, but you would have to make a concentration check or lose the usage.
According to the SRD on SLA:
And then under their section for Grappling:
Yes, you can use spell-like abilities in a grapple.
Spell-like abilities, amongst other things, have no somatic, verbal or material components, making them suitable even in situations, such as grapple, where you're prevented from acting freely.
Mechaniclly, my deductions work on three levels:
Glossary: RAI: read as intended, as contrapposed to RAW - read as written. SLA: Spell-Like Ability
No, you can't.
This hinges on the actions one can take while grappling being specifically listed. Using a spell-like ability is not among the listed options.
The alternative reading (used in Zachiel's answer) is that the list of options only mentions those standard options it modifies (such as "attack your opponent") and those it adds, but does not exclude others that would be normally available to a character. I find this reading problematic, on account of it allowing actions the rules can't handle ("what happens if a character decides to take a 5' step?" comes to mind). Also, D&D 3.5 very frequently uses this model to determine the scope of the rules - listing what is possible, leaving the undefined actions as impossible.
This is what I believe is the most correct application of the rules. For what I personally feel makes the most sense, I refer the reader to the other answers.