I think you'll have to sign up but it's free and quick - I can't remember but I don't even think you need to do email confirmation.
Did they change Danbooru or something? I was enjoying it for many many weeks and then all of a sudden I kept getting a login message and when I did it would, it would say that I needed to sign-up, and I finally got pissed off and stopped going to it all together. Now, I'm not having any problems and I'm so confused :? .
Well the only issue I'm aware of is the server keeps being overloaded and it will keep asking you to wait for a minute and let the page auto-refresh. It's pretty common for it to say that, particularly if you're browsing in more than one tab.
There's also http://gelbooru.com/ which is essentially a clone of Danbooru (in terms of style and content) but has the difference of allowing loli and shota content to be seen by all members, not just "privileged users". It used to be slower than Danbooru but now that Danbooru's server seems to be on its knees, Gelbooru is actually the faster option.
Wow I must be lucky. I've been wondering all week if there's any Makoto hentai out there are someone also seems to be thinking the same thing. Let me know if you find any others buddy, and maybe some Ibuki too.
Also, thanks for those two links guys, the first one is (like you said) having the server overloaded message so I haven't had a chance to check it out yet, but that Gelbooru place is pretty sweet.