There's a forum I'm in that was discussing someone's top 10 anime list. I've seen a lot and it's quite difficult to narrow the expansive library of what I've seen down to 10 titles. There's a lot of good out there, and a lot of not so good. Like any list, things will get left out that you'll want to include. It's almost inevitable.
So instead of doing a total top 10 list, I'll be doing top lists by genre. I won't limit to a specific number since some things just don't need to be listed and others probably need some attention. Within the lists are no specific order since it's just really hard to pick one over another because they might have a general theme related, but not necessarily the same overall feel.
TOP SPACE ANIME
1. Moonlight Mile - Really sad this only had 2 seasons. It was highly realistic and had some great characters and motivation. The designs were rough but true to the manga design.
2. Irresponsible Captain Tylor - Space comedy! You wonder how someone as inept as Justy can get as far as he did - if it was luck or if he's a savant, but ignoring logistics, there's a lot of charm and excitement to be had.
3. Cowboy Bebop - If you haven't seen this, WHY? Action, drama, comedy, amazing musicGo watch this now.
honorable mentions to Kiddy-grade and Bodacious Space Pirates and Outlaw Star.
TOP MECHA-ISH ANIME
1. Rahxephon - When I watched Rahxephon, it was shortly after a full marathon of all there was of Evangelion at the time. And the only thought we could all think of was: This is what Eva SHOULD have been.
2. Big-O - It's cheesy, almost Gotham in appearance, and really confusing, but there's something that just attracts me to it. Maybe it's R. Dorothy and her dry wit.
TOP FANTASY ANIME
1. Slayers - There's a lot of slayers out there and it rarely disappoints. It's got a ton of comedy value, over the top spells and an ongoing motive to keep you involved.
2. Bastard!! - It's a short OVA series that isn't for everyone. It's completely over the top in every way.it breaks the 4th wall, has equal opportunity nudity and it's ridiculous in a good way.
3. Tower of Druaga - Full of your typical fantasy cliches, it's still an entertaining watch. Holds more value if you're familiar with Namco's RPGs.
TOP CYBER/STEAM PUNK
I'm not even sure how this category really goes, but I think some of these things fit here.
1. Last Exile - Some really marvelous design work and an enthralling story of how a few kids get caught up in war. It's follow up wasn't bad at all either.
2. Texhnolyze - This is also not for everyone. It's dark, gritty and really hard to explain. Yet for some reason I come back to it every few years.
3. Ghost in the shell: Stand Alone Complex - I've seen this identified as cyber punk, so I'll just put this amazing work here. Really detailed story, great characters, beautiful animation.
TOP COMEDY ANIME
1. Gintama - This show. It has a lot of obvious and not obvious parodying, but it holds its own even when it doesn't resort to that. Even the serious arcs are wonderful
2. City Hunter - Not a straight up comedy. More of a comedic cop-type show, I suppose, but there's rarely a scene that goes by that doesn't have some sort of humor in or shortly after it.
3. Sayonara Zetsubou Sensei - This show requires a fair amount of Japanese cultural knowledge. and a pause button. But worth it.
4. Polar Bear Cafe - My new favorite thing. It's not always laugh out loud funny and sometimes the puns induce severe groaning. A little familiarity with Japanese culture will make the puns even funnier.
Honorable mentions: Excel Saga, Danshi Koukousei no Nichijou, Azumanga Daioh
TOP SLICE OF LIFE/FEEL GOOD ANIME
1. Natsume Yuujinchou - Slow paced, occasional action or suspense, but nothing terribly heavy, and a hint of comedy. Somewhat episodic.
2. Kids on the Slope - About some High School kids in 1960 s Japan and their love of music and relationships together. Feels almost real.
TOP UNCATEGORIZED ANIME
I didn't really have other things for whatever categories they might belong to - and they might have overlap above. But I'll put them here instead.
1. Detective Conan - A lot of episodes are disposable but if you collect the few hundred that aren't, you have one amazing detective story. The arc in the late 400s(?) with the clash of Red and Black is the pinnacle of the story so far and just opens things up wider.
2. Full Metal Alchemist: Brotherhood - Better than the first FMA, this follows the manga closely and does a really good job of it.
3. Rose of Versailles - A few different perspectives of Revolutionary France. Done masterfully and with really great characters. Oscar is probably one of the best women in anime.
4. Trigun - Anime meets outer planetary old west and does a bang up job. Also, has donuts.
5. Tiger & Bunny - Corporate sponsored super heroes! Fun characters and action and interesting story to boot!
I'm probably leaving out a lot of things I like, and while there are things I like a lot (Nerima Daikon Brothers, for example), they're certainly not the best. I also realize I ignored the Harem genre, but there aren't really any I'd say anything above "that was fun, but not really a top watch".