Trying to get into assassins..im pretty focused on support/tanks though like maokai..any suggestions?

evelynn with boots +5 is amazing

Some great assassins are Akali, Kennen, Talon. Akali is probably the hardest to use out of the bunch but is a very effective 1v1 assassin. These champions have quite a bit of mobility which helps them to be in and out whenever necessary.

-RyuTres

Talon is an amazing burst and 1v1 champion, once he gets Boots of Mobility(depending on the lane), Bloodthirster, and Trinity Force. You can nearly burst down anybody quick except for true tanks.

Fizz is a fun assassin. Trollpole ftw.

I actually disagree with the Red here.
Ken in my opinion is the hardest of the assasins that he mentioned, as Ken is the only one with a skill shot, and to play him properly you need to count his marks.

however talon is a blink to enemy unleash and run away. (or continue to fight if you are certain no one else is around)

And Akali, well she is squishy as hell, especially before 6 with no get away. But good positioning and she will tear shreds through the enemy's back line. I have 4 penta's to my name, 3 with akali.

Since you mentioned that you like to play tanky champs, perhaps you would like Poppy? She is classified as an assassin and when played right she is downright scary as hell.
Of course, if you want one of the other's mentioned by RA, a just something to note about Talon: he ooms, really hard if you're not careful. Ever since his nerfs a while back, he has had a somewhat troublesome mana issue. Yes, as I'm sure someone would point out, it was put in place to keep his W in check since it was very spamable. But, the extra cost they added on to it along with the mana regen reduction has made it so that in order to keep up harass ou would need to build a philo stone. This however hurts his damage alot early game, which is bad for assassins, especially talon. So to counteract this mana need, you gotta get mana regen runes and take the place of your armor which is really risky since you're so squishy to begin with.
TLR: IF YOU GET TALON, GET READY TO OOM AND NEED MANA RUNES. SO GET KENNEN INSTEAD =]