Without a doubt Outlaw Star, Gundam Wing, Black lagoon, and though it may ruin my childhood memories, Ronin Warriors.
I would totally re-watch Clannad and it's sequel(again and again and again). I love that series! Also Hyouka. I'm quite the KyoAni fan. I want to watch TMoHS but I kinda don't like to watch the endless eight all over again! You might say I can just skip it but I just can't skip single episode on any series I watch.
I'm definitely with you on watching Gundam Wing again. I didn't really understand it as a kid, so I hoping to understand it now as an adult.
For me, I'm planning on rewatching Hikaru No Go (it got me into playing Go), Cyborg 009 and Seven Samurai.
The characters, drama and romance, for me. I like how the story progress and ends up with. Tear-jerker type of anime.I never watched Clannad, whats the big deal with it?
When I first started watching anime, I had begun watching Naruto. I was a bit confused with how some episodes didn't follow up on the stories of others. It was only after i had watched hundreds of episodes that I realized most of it was filler. I think that if I were to rewatch Naruto with no filler episodes it would be quite fun.
It's probably the biggest reason why I dropped the anime lol. Finished reading the manga already, but the anime was still a few arcs behind, having more filler episodes than story episodes! Rewatching it with no filler would definitely be much more enjoyable.