Very old animes, in my opinion are: Mila Superstar, Lady Oscar and Cats Eye,
all three of them are just great^^!

a good old anime i would say is yu yu hakusho

UFO Robo Grandizer, Starvengers (Change Getter Robo), Yamato (Starblazers), Science Ninja Team Gatchaman (Battle of the Planets, sort of)

If you haven't watched Maison Ikkoku / read the manga, you should.. Probably one of the best early love triangle type animes ever made (IMO). I like that particular type of anime so that's why it's my fav ^^;

I would recommend:
Yu Yu Hakusho
Rurouni Kenshin
Trigun
Full Metal Panic
Fullmetal Alchemist

The only few 'old' animes I have watched are Pretear, Rurouni Kenshin, Flame of Recca and Sailormoon. These 4 titles are really nice (at least in my opinion).

Besides, some old ones that I know are nice but I haven't watched before are Chrno Crusade, Neo Genesis Evangelion, Kaleido Star and so on...

My favorite classic anime is:

Armatige III:Polymatrix

Bbattleangel(out of print)

Vandread

Berserk series

I did remembered this great old times like Yu Yu Hakusho, GPX Cyber Formula, Yu Gi Oh! Duel Monsters, and Patlabor too.

Record Of Lodoss War- It's an anime tribute to Lord of The Rings (way before the movies were ever done)
I recommend the 26 episode version.

Try BlackJack, the medical mystery series by Osamu Tezuka (he did Astroboy, I'm sure you're heard of it It's very sensible with a good sense of humor and drama, kinda like Detective Conan.

Some older titles I enjoyed...
CLAMP's X ****
Fushigi Yugi
Chrono Crusade ****
Yu Yu Hakusho *****
Rurouni Kenshin *****
Samurai Deeper Kyo ****
Scrapped Princess
Witch Hunter Robin ******
Escaflowne
Pretear
Midori Days
DN Angel
Fullmetal Panic, Fullmetal Fumoffu, Full Metal Panic TSR *******************
Mai Hime
Hellsing
G Gundam
S Cry Ed
Wolf Rain
Madlax
Blue gender
Noir
Crest of the Stars
Elfen Lied
****Trigun
Chobits
Saikano
Ai Yori Aoshi
Ah! My Goddess