Elfen Lied left an impression on me.
Mostly an impression that it's not hard to piss away all the potential for an anime in a few, short minutes. Usually it's a good hint that the anime is going in a bad direction when the original creator isn't involved and the director decides that the anime plot line is bad and then proceeds to liberally amend it.
Beebop is your quintessential anime. High production values, an insistence not on catering to the otaku crowd too much, great plot line and generally just believable. Outlaw Star comes in a close second, but mostly because it fails to meet those same expectations. Trigun is worth mentioning too.
Evangellion is some hot shit too. You can't not watch that and not feel something. Probably either rage at the ending, or depression at what leads up to it. Do not marathon this- it's a skull fuck in the most literal of senses, and if you disregard what I say be prepared to go digging. After the initial series they released a few movies (Death and Rebirth) that amends to plot line that had to get cut amongst a dwindling budget and general criticism for the content of the anime.
And appropriately Gurren Lagan is a highly appropriate anime to watch after Evangellion because it symbolizes a revitalization of sorts for the whole mecha genre and an awakening from a depression that Eva set into.
