Cowboy Bebop is forever frozen in time (no debate) as #1 for me, with honorable mention of Fist of the Northstar for the old-school stuff.
Rurouni Kenshin (season 2) is the arguably the best combat anime of all time.
JoJo's Bizarre adventure, all seasons belong in any top 10 list.
Also, love Blade of the Immortal.