Fullmetal Alchemist brotherhood is always a good start, especially if you're into action series. it's 60+ episodes .
if you're looking for something similar but a bit shorter, there is the Space Opera "Cowboy bebop" at only 26 episodes and an amazing soundtrack, though keep in mind this is an anime from the 90s so the artstyle is a little dated.
and for something a little more recent "Attack on Titan" a fantasy where humans fight for their survival against giant monsters, same length as bebop though there is a second season in the works so there will be more episodes later.
If you're looking for something a little more light hearted and just want to enjoy a good laugh or 2 then I give you the following recommendations.
First off is "Toradora". If you are a fan of romantic comedies this is probably the best start for anyone, featuring the everyday lives of a tiny girl with a short temper and kind boy who always gets mistaken for a delinquent, same length as bebop and Titan
and also there's "The Devil is a Part-Timer". A much shorter anime at around 13 episodes. It's a humorous tale where the Prince of Darkness himself Satan, get's stuck in the mortal realm and in order to survive he needs to get a job at McDonalds.
All of these anime are english dubbed, and a lot of them can be found on FUNimation where you can sign up for a 14-day free trial to watch as much anime as you want. if you're looking for a free streaming site then what you're looking for can be found by google searching "*name of anime* English dubbed" and it should give you a list of streamable sites for your viewing pleasure.