1. Higurashi no Naku Koro ni - This is one huge mystery-fest that just baffles the mind. It's one of those animes that really makes you go "WTF" several times. Whether it's the gory, bloody scenes, or it's the spine chilling atmosphere, right down to how downright creepy the characters can get...or at the weird and wonderful club activities games and the punishment game that ensues, the intensity is off the charts. The whole mystery of the Hinamizawa chain of deaths is huge, it's keeps the viewer hooked wondering who or what is behind them.
2. Detective Conan - I started this roughly a year ago, it has taken me a year to get through 651 episodes, 15 movies and all the other various spin-offs, OVA's and Specials. I love this anime almost as much as Higurashi. Similarly to Higurashi, there is a mystery element to it. Although, this is more in the form of....well actually the same kinda mystery as Higurashi: murders. It's always exciting to see how the culprit's pull off their tricks in their cases and even more exciting when Conan unravels them. The action is always exciting, and leaves you in suspense.
3. The Melancholy of Haruhi Suzumiya - This anime always has a special place for me, it was officially the first anime I ever watched, and was the anime responsible for kicking off my love for anime all those years ago. One of your typical Slice of Life animes that sets the bulk of the story in a High school. What's not-so-typical is the story. It's the story itself that really kept it going for me, and the array of well designed characters that fit the plot perfectly. Season 1 started the series off really well, I love the narrative by Kyon. Season 2 is debatable amongst fans, because of the Endless Eight saga, but I am one of those few who actually loved it because it made you feel frustrated at watching what seems to be the same episode over and over again, essentially feeling (to a lesser extent) what Yuki Nagato felt during those 15,000+ repetitions of the two weeks of summer. The Disappearance of Haruhi Suzumiya movie was pretty much perfect, matched the Light Novel/Manga really closely and it was put across amazingly.
4. Clannad - A great example of an anime that clearly had a heart and soul put into it. A real tear-jerker, which is full of moments that can make you laugh, and relate to the characters. I have never cried so much with any other anime before watching Clannad...heck with any TV Series, or book or movie or anything really. It really made you feel for each of the characters, get angry when they do laugh when they do, cry when they do, it's really effective at what it aims to do.
5. K-ON Another anime which has a heart and soul in it, except this time in the form of music. The focus on K-ON is on the characters and the Light Music Club. I must say that the characters are adorable. Each has their own unique personality and traits which make them as interesting as they get. The anime itself is really light-hearted, with no particular seriousness to it, but the one thing that makes it stand out as an anime, would be the music itself. Since it's centred around a band, it's logical to assume that the songs featured on there are going to be pretty damned good...and it doesn't disappoint. I love each and every song that comes from K-ON. The Voice Actors/singers really put their all into it, and it radiates. Anyone who watches this will fall in love with Yui Hirasawa when you see her, she's probably one of the most loveable character of all time.