I managed to light up 88 10mm clear lens ( no datasheet, I assumed 3.2v, 40ma ) blue LEDs (using appropriate resistors for each one of them) with 5v off 'hotwiring' a PC power supply. The room is all blue now! Thank you for all the info!

Now I'd like to make a strobe with it, with a pot to control the strobe intensity.
What's the best way to do it ? TRIAC ?
I've been told I can't use the 555 because of the amperage limitation.

Thank you !

I'd suggest using a big FET or solid-state relay to switch the current, so that you can use a low-power signal from a 555 (or such) to control the higher current.