The talking goat is nice as well.
And wasn't there a couple in Max Payne as well? Some hidden office with (among other things) a couple of posters for Soldier of Forune or something. (Fuzzy memory, gotta play it through again some time)

Max Payne had several. There is also a room where you could only get by entering another room, climb out of the window and walk over a ledge to the next room.
Once you entered it there was a man on the floor with a stake through his heart. On the floor "Buffy" was written in blood.

We have the Internet now. There are no secrets after the first person finds it.

You're right Syme, but i think you will search for the secrets on the internet only if you won't bother yourself with searching (only if you know that game has some secrets).

couldn't you get the most powerful weapon in Wolf3d simply by turning around on the 2nd level and blasting the walls?
I used to love the secrets in Wolf3d and Doom because it was a challenge to guess where they would have placed them... there was often a logic or a pattern to the placement, or very slight hints... but it sure wasn't easy.
By the end I could look at a room and say "there will be a secret there".
I used to love finding the bacta tanks in the most out of the way places in jedi Knight too..

One of the reasons why Fallout 2 is the best game ever.
Random encounters.

I still rate Blood as the game with the best use of (and probably number of as well) secrets. The lesser secrets were always fairly easy to find - you'd rarely walk through a level without bumping into at least a couple. Then there were harder and harder to find secrets ranging all the way up to real super-secrets that could win you the game if you found them.
Duke3D was much the same thing and a big reason I got it from GoG. Apart from that it rocks.
Are there other games on GoG that have a farily steady supply of secrets? I know Painkiller has some.

While I do miss having secrets in games, I really miss those days when the games weren't locked and you didn't have to play the damn thing a million times just to unlock content.

MUDs are pretty good at keeping secrets. Not that too many people play MUDs, but most MUDs don't like it when someone makes spoiler sites. I'm playing Aardwolf for example, and there's barely anything out there about it except for some equipment lists and a map or two.
Also, if you ask about certain quests on the MUD, you won't get too many friends :)
It used to be the same in EverQuest until Verant changed their mind.

Max Payne was full of little easter eggs which I loved - I remember vividly one of the comic cut-scenes where Max Payne imagines himself in a video game, and also him saying "Thank you!" after I shot the speaker during a long elevator ride.

Ah secrets secrets. I miss them, too. Actually, I don't think I've played many games recently that could have secrets in them... mainly because I've been doing plenty of multiplayer and RTS, so secrets just don't work with those games.
Anyway, some favourites of mine are:
Dopefish in Quake 2
Dopefish in any game :D
"Moon" secret in Keen 4... where you stand on that part in the pyramid and keen moons you! :O
Wolfenstein level in Doom :D Friggin awesome
Serious Sam, holy crap this game had the most amazing secrets. I remember seeing a giant pair of eyes floating in the air... (so creepy, but surprisingly easy to miss) but a giant guy appears when you shoot them! THEN HE EXPLODES. Insane.
The game that disappointed me most was Half Life 2. It had so much potential for awesome secrets, what with the gravity gun and the ability to "pile stuff up". I actually got to some places I wasn't supposed to but there was nothing :( So disappointing!
Anyway the secret that gets the cake is DOPEFISH. Holy crap, it blew my mind to see so many games that have DOPEFISH in it as a secret... Jazz Jackrabbit, Max Payne, Quake 2, Duke3D (check it out at dopefish.com) etc. I wish more games these days have the DOPEFISH SECRET

Psychonauts and SiN also had the Dopefish, if my memory is correct.

Yes I have to agree that there were some good ones in F2, as a Dr Who obssessive, I was glad to see the TARDIS.
I remember that easter egg in GTA Vice City that was a literal easter egg

Dark Forces.... The Ewok on level six that you could only find by combining cheat codes. Though I never did find out how to get those three extra lives on the last level.

Ewok? Seriously??