Let's see... I've actually watched Gundam Wing (Up to episode 19 anyway. I got fed up of downloading it at that point...) and Neon Genesis Evangelion, which was fantastic. Especially End of Evangelion... One of my favourite films. Evar. Akira is just a classic, if not a bit freaky. Again, heard good things about Ninja Scroll, but never quite got round to tracking down a copy. Ditto for Shadow Skill. Tenchi Muyo I know of, but little about. Sonic, I liked when I was younger, but don't seem too keen on any more.
Excel Saga is fun, too. But I prefer downloading more recent stuff; heck, if you've got broadband, you may as well make good use of it. Although hard-disk space tends to be another limiting factor. Still, I've watched a few other series all of which are worth following up, if you're able; Scrapped Princess Kimi ga Nozumo Eien Full Metal Alchemist Kanon Full metal panic (Fumoffu!)
Kinda pathetic, really... But they're all good. Cowboy bebop ish teh rock as well, though. Rar.