Hmmm...  I think the Cloaking Eldar fleet I played for a long time was the most tactically interesting one I've seen.  It really made both me and my opponents think.  At first I had the advantage, since they were unprepared for ships decloaking right behind them.  The first time I fielded them, it was in a 2v2 game where I was allied with the Imperials from ISS.  I cloaked, the Imperials were slaughtered to a man, and then I decloaked and managed to pull off a draw.  It was beautiful.  Then they started making one-hexside turns to bring their side guns to cover their rear arcs, so I started having to anticipate which way they'd turn and come in from the other side.  Probably the crowning moment of the cloakers, though, was when I cloaked, the enemy closed for two turns and then off-lined since they expected me to de-cloak behind them.  I, however, hadn't moved at all, so I decloaked right in front of them...  exactly where they weren't expecting me.  Their facial expressions were priceless.

So, not strictly a tale of tactics without ship design, but definitely a series of cases of ship design enabling tactics.