Vash the Stampede, the wanted man of 60,000,000,000$$
If you are a die-hard anime fan than no doubt you have already seen this one. If you haven't already, shame on you! Go download/buy/borrow it right now! Trust me, you will not be disappointed.
Trigun is a very traditional anime, but at the same time very good. Traditional in the animation techniques used (it was made in 1998 and computers were back than not yet such an integral part of animation as they are right now), which are definitely not bad, visual speaking this anime does even now after 15 years still look amazing. If you have seen a lot of anime than you will definitely recognize some of the visual art tropes this anime has that are unique to anime (For more information about those take a look here: http://tvtropes.org/pmwiki/pmwiki.php/Main/JapaneseVisualArtsTropes ).
What makes this anime stand out from the crowd is the story. The mood you get from this anime during the first half of series is that Vash the Stampede is really on a desert planet in the distant future. It is definitely a cool mix of the old American western culture and a distant future with cool technology where human colonists set out to colonize other planets. The first half of the series is without a doubt a hilarious, action-packed, phenomenal and awesome piece of artwork you will not soon forget. The stories are really of a fantastic quality.
The second half of the series is where it gets serious and where (in my opinion) the anime loses some of its quality story-wise. Its still good, but the fact that Vash is portrayed as some kind of Messiah that walks the earth trying to undo his errors from the past and who's life-motto is to do no harm under any circumstance gets to a point where it becomes annoying and makes him look like a pathetic douchebag not worthy of the enormous bounty on his head (For example, at one point in the anime in an attempt to save someones life he strips naked and barks like a dog in front of a group of thugs he can easily take down).
Nevertheless, This together with Cowboy bebop (http://trakt.tv/show/cowboy-bebop
), Neon Genesis Evangelion (http://trakt.tv/show/neon-genesis-evangelion
) and to a lesser extent Berserk (http://trakt.tv/show/berserk
) are the anime series from the Nineties that every fan of anime should see at least once in their life time. Without these on your watched history pages here on Trakt the term Anime Otaku does not apply to you ;)