Gintama's quite long, and personally I couldn't take it. But it's something I'm not catered towards so, go ahead it's solid and great.
I'm unsure as to you've the GUTS to watch them, but I will suggest a few classic's.
Berserk by Kentaro Miura, of course you should be watching this in the English if you can help it, as the setting and voice work really works for this series. Set in the most Medieval Fantasy Europe, follows a young mercenary and his interactions with the Band of the Hawk, a rag-tag mercenary group. 26 Episodes, and I do insist you get past the first episode. Every time someone starts up episode 1, they don't see the appeal, but you can't get past 2 man, it just throws you in. The series is quite old and by all means PURE TESTOSTERONE!
Next up I'll suggest Neon Genesis Evangelion. That one has quite a reputation, I still suggest English here as you've got a lot of dialogue to be hearing, and you get to focus more on whats happening and less on reading, which quite important in this highly story driven anime. It REALLY shines when you watch it with a sibling or friend, It inspires you to talk about it, you'll pause and just talk about what happened for an hour before you actually play it again.
I'll throw in Trigun as well, A grand favorite and far easier to get into than the previous two. Just watch it, you'll have more fun in these 26 than you should. Also contains a recently(AND AMAZING) made movie which transpires during the series, made ONLY because of the overwhelming love Westerner's have for westerns, not too popular in japan for some reason, I don't know why.
Man this is getting long, but I like to inspire you to watch some of these so here's more. "Clannad" is on the exact opposite of the other series. Japanese Sub's be fairly common here, it's your choice. It's not manly or exciting. It's just one of those Moe series done well. Just take the evil, evil, evil stuff in the other series, and make it super-ultra-cute, with lots of bleach to remove blood stains, here you go, one Romance that actually pays off, makes you really sad BTW.
Other staples that I couldn't do justice and I'd have expected it already watched include FLCL, Tengen Toppa Gurren Lagann, Samurai Champloo, Spirited Away (Greatest Animated Movie ever), and Batman the Animated Series (Of freaking course)
For a more close to home yet (a little)more obscure, I suggest these final two.
The Slayers - 4 Season's, Three in old school DBZ's 80's-90's animation, one Blue Ray'ed HD'ed Season 4. Solid show for those into the Swords and sorcery with great comedy thrown in.
Ranma 1/2 - A Boy turns into a Girl when he's doused with Cold Water, and back into a boy with Hot Water, HILARITY ENSUES. Lots of martial artist wackiness and hilarious characters. 7 Season's, 3 Movies, 12 OVA's.
Oh god, I just want to go on and on here. I'm rewatching Yu-Gi-Oh GX in Japanese right now, but damn it I've too many suggestion's than you could possibly watch.
Panty and Stocking with Garterbelt, an anime made just so the Japanese voice actors could ask the English ones to teach them new English cuss words.
As you can see, I'm big on Gainax.