Recommended way
The standard logger in symfony would be the recommended method:
from inside an action:
$this->logMessage('executed SQL: '.$sql);
from inside the model (or anywhere else):
sfContext::getInstance()->getLogger()->info('executed SQL: '.$sql);
These methods would insert your SQL queries into the 'logs & msgs' tab in the debug toolbar in the correct position in the execution chain.
However, if you just want to see the queries at the top of the 'logs & msgs' tab and don't need them to be stored in the permanent log, you can use $this->debugMessage($sql); instead, which would also mean you could see the queries together, and not search for them through the log execution chain.
A potentially preferable way
I suspect that you may want these SQL queries to appear on the 'DB' tab instead. This isn't directly supported by symfony, but you could 'hack' this solution instead:
from inside an action:
$this->logMessage(sprintf("{sfCreole} executeQuery(): [x.xx ms] %s", $sql));
from inside the model:
sfContext::getInstance()->getLogger()->info(sprintf("{sfCreole} executeQuery(): [x.xx ms] %s", $sql));
This mimics the behaviour of the debug option in symfony for logging SQL queries, and will therefore push your custom SQL query into the 'DB' tab in the debug toolbar. I leave the timing [x.xx ms] option up to you to implement if you wish it :)