Hey mate, I feel your pain – that registration nonsense kills the vibe every time.
These days one of the better no-strings options I've stuck with is easyplay.vegas – they've got a pretty big free play slots section with zero signup required, you just load the page and start spinning. Decent mix too, from classic Vegas-style ones to some newer themed games with solid animations. No malware crap or endless ads popping every spin either.
Give it a go if you're after quick casual play without handing over your soul lol. What games are you hunting for specifically? Might have more suggestions.