Beelzebub is now over and I'm in withdrawal already. Are there any good replacements like it?

Depends on what u mean by "like it" you want a supernatural fighting manga or a demon fighting manga o,o any specific genres u want or want to exclude? depending on your answer i have quite the suggestions.

Also do you want a complete manga or ongoing?

Supernatural fighting would be great. I'm already reading Ao No Exorcist.

I prefer Ongoing, but will accept Completed if it's good.

Kekkaishi
Nurarihyon no Mago

hmm super natural....

Rave Master :Rave master was one of the best manga's i have ever read in my life, it had good fights and a fantastic story plot, it was made by the same mangaka that is writing fairy tail, however in my opinion fairy tail cannot hold a candle light to Rave Master.

Immortal Regis :Immortal regis is a good manga, it ends at about chapter 40 but then is picked up by its sequel, the story plot is good, how ever in my opinion i kinda didnt like it that much cause of some tragedy in it, however if you dont mind tragedy in the manga, its a good suggestion.

Nanatsu no taizai :this manga has an interesting plot, decent artwork, and is still ongoing, i started reading it recently, but now i cant wait till latest chapter.

The God Of High School This is actually not a manga but a webcomic, however its rather good with an easy to follow story plot, and best of all its colored and still weekly ongoing.

Yumekui Merry ....: THIS!! I honestly don't know why but this manga felt like it was one of the best manga's ive read in a long long time, when i found it in some suggestions i instantly picked it up, and ended up reading all its chapters up till the latest in 1 day! the artwork was amazing, and story plot couldnt have been better.

Mahou Sensei Negima! : This isnt much of super natural fighting, but is acutally more towards magic, the begining felt super boring to the point i read a couple of chapters then decided ill finish it later, however after about 30 chapters into the manga, it started getting really interesting, it had a decent plot that u could easily follow through and sometimes you can expect whats going to happen, its a long manga about 300 chapters and completed, but definitely worth a shot, also after it was done they started a sequel for it, UQ holder! It isnt a direct sequel, rather indirect, u can read the sequel without the original and still you would understand the story.

Black Cat :Black cat was one of the only anime's that they aired in my country, upon watching one episode i decided i'd go read the manga, and to my surprise it was extremely good. its definitely a MUST if your into the hit-man organization type of manga's.

Soul Eater : I picked up reading this manga from all the forum post suggesting it, upon reading it the plot kept getting more interesting, i ended up reading non-stop to the point i reached up to the latest chapter in only 2~3 days. It ended a while ago but was still interesting, i suggest if you have more free time to read this. Also it's anime was rather good, but the ending in anime and manga were different.

Code: Breaker : this manga was rather boring when i first picked it up, the heroine pissed me off to no limits, she kept talking about righteousness in dire situations, how ever after a while it seemed that she "grew up", The manga's plot was good, it kept getting more interesting, and there were lots of good plot twist, it ended about a week or 2 ago (the scanlated version) but was alright.

Those mainly were the ones i could find in my ongoing and complete list, there were more but i felt these were enough, if u want to find some more try checking my ongoing/complete list. i got tons that still might suit ur tastes, if your tastes were similar to mine o,o 😀

Nice list. If you have some more, I could use some more to keep me busy. 😀