Thanks @Vlad and @[deleted], you two were really helpful! <3 I think I'll start with Ergo Proxy then.
@Camo Yoshi
Ano Natsu de Matteru - I really liked this one. Despite being a simple enough rom-com, it had its shines and got resolved pretty clearly. However, before watching this one, I'd suggest trying Onegai Teacher first. There are obvious similarities between the two, both of them were written by the same person and, at the end of Ano Natsu, there is something that links two of those anime together. No spoilers though~
Wherever I go, Great Teacher Onizuka gets recommended time and time and time again, and for a good reason - it's a very very solid anime. Just read idek's post.
Nagi no Asukara - ughhhhhhhhhhhh. This one is tricky. I wrote a review on it, it's split in two parts, but I wouldn't recommend reading it if you didn't watch the anime... I guess? Well, in short, I fell in love with this anime and then my love was crushed. It has an unique concept, tackles some serious issues and is a great watch altogether, but you'd better prepare for the ending. So yeah, watch it, if only to discover how great a setting it's put in.
Nisekoi - if you're fine with anime that never seem to end, pick it up, if not, just lay it off until they decide to finish the story. It's a great comedy with some quality character designs, but overall, it's 'just another rom-com' in the end. That is, until they bring it to a conclusion, which they didn't yet.
Steins;Gate - an indirect sequel to ChaoS;HEAd and an indirect prequel to Robotics;Notes. While ChaoS;HEAd isn't really worth the watch and isn't even required to understand the story, and I didn't watch Robotics;Notes yet, Steins;Gate remains one of my favorites of all time. Butterfly effect, time travels and its consequences (yes, you'll really love them - for example, a trap stops being a trap and becomes a trap once more!) and a legitimate, finished romance to go with it! Pretty much a must-watch for me.
Toradora! - must-watch in terms of romances, nuff said. Just watch it, no questions asked. They really put an effort to making this anime a success and it paid off - from the great story, through nice visuals to the awesome ending. Also, yeah, once you get to the last episode, watch the post-credits scene.
@[deleted]
Shiki is pretty good, the ending especially. Finish it ASAP.
Sankarea - pretty fun overall, rather unique setup with a zombie, worth the watch.
Kiss x Sis - manga is better from what I've heard, the anime is pretty okay as well, but OVAs are where it's at. Seriously. If all you want is getting aroused by an anime, this is your go-to.
School Days - I would rather not. I really would rather not. Unless you like MCs so shit you can't even feel empathy for them.
Maken-Ki! - boobs. fight. torn clothes. boobs. superpowers. boobs. Fun to watch you're looking for simple action with boobs.
Freezing - as above.
Sekirei - as above. The second season of that, however, is way better than anything else of the sort you'd compare it to.
Ichiban Ushiro no Daimaou - as above. I really enjoyed this one, personally.
Hyakka Ryouran: Samurai Girls - as above. It has better plot and a more original (borderlands-ish) artstyle.
Gokujo - short, fun and lewd. Had its ups and downs, overall a pretty good watch, if you don't mind a few boring episodes.
Kimi ga Aruji de Shitsuji ga Ore de - I really need to rewatch that one, but from what I can remember, it was a really nice anime.
Nozoki Ana - don't bother with the anime, the manga is where this truly shines. I cried at the ending.
Dakara Boku wa, H ga Dekinai. - ehhhhh, no. There was a time when I enjoyed it, but after trying to rewatch it recently, I couldn't make it past episode 8. It's just too dumb.
Machine-Doll wa Kizutsukanai - fun to watch, disappointing ending, but overall has some nice moments, if you can forgive the slow start.
Seirei Tsukai no Blade Dance - no. Tsundere kills the whole show. Unless you like extremist tsunderes.
Saikin, Imouto no Yousu ga Chotto Okashiinda ga. - ehhhhhhhhhhhhhhhh. Really, now? I'm at a loss for words regarding this anime. One of the more 'original ideas to create an ecchi series and instead it gets borderline, pointlessly so. Just... if you feel brave, try it.
Zero no Tsukaima - four seasons, watched them all, very pleasant surprise. Comes to a clear conclusion and the heroine, despite being a tsundere, is lovable. Worth recommending.
Trinity Seven - a pretty fun ride, nice setting and seven heroines to choose from. Too bad it's cut at the suspense moment.
Hentai Ouji to Warawanai Neko. - if 'cute' is all you need, this is your best bet. If you want any plot to go with it, though, I'd suggest Sakurasou.
Yamada-kun to 7-nin no Majo - kissing, kissing, kissing! The abundance of that, nice plot, and the story does finish! Recommending for sure.
Date A Live - a fun ride indeed, I just wish they gave the main heroine more screen time. But yeah, very nice overall.
IS: Infinite Stratos - indecisive MC, mecha-like things and rom-com stuff going on. Pretty fun as it goes, but gets old rather quick.
Durarara - watched the original one, I loved it. Didn't see the newest ones yet, but I'll get to them soon. Just... An Ikebukuro trip for everyone! With gangs, mysteries and such.
Guilty Crown - not too bad, but not good either. Soundtrack is the best this series has to offer. And at some points, the plot will just spit in your face.