Devil Crash/crush is a great pinbal game with really great music.
Kyukyoto Tiger - helicopter shmup by Taito
Legend of Hero Tomna - great platform arcade
Ninja Spirit - another great arcade conversion
Takahashi Meijin no shin Boken jima - this is basically Hudsons wonderboy clone and its hard game!
bikkuriman world - another wonderboy clone and one of the early pc engine releases.
Dragon Spirit
Dragon Saber - sequel to dragon spirit
Magical Chase - if you can afford this one its cute shmup with a witch made by quest. Supposedly ex-square staff's first game before they went on to make the Ogre battle games.
Parodius da!
Detana Twin Bee?!
Gradius
Salamander - aka life force and this is one of the hardest shmups you will ever play!
Raiden
Aero blasters
Mr Heli no daibouken
Hana Tahka daka!? - aka super long nose goblin shmup by taito
Bomberman
Bomberman 93'
Bomberman 94

There's probably a lot more to list but im gonna pop back onto Fable 2 XD

EDIT oh please if you like god sim games get Populous its a great conversion by Hudson soft and menus are in english

Thanks for all the suggestions, some that I used to own, but many that I didn't. Will keep an eye out for them.

I'm thinking the CD-Rom add on will have A/V built in right? If so I might just buy one of those instead of getting an A/V booster.

yup. they have A/V composite connectors

Also the white pc engine I have I find the audio crackly.. I wonder if this is due to corrossion of the hardware.. ah well at least the core grafx II sounds like how it should

R-type 1 and 2, Ninja Spirits, Bonks, Blazing Lasers- Gunhed,Wonder Boy 3, Demon Castle Drakula X, Snacher, Alien Crush, Phantasy Zone, Side Arms, my brain hurts trying to remember these..

oh the other thing.. the original pc engine only had an RF connection. The later re-design of the core grafx and core grafx II had 5-pin connecter with A/V connections for red, white and yellow

So I'm thinking of getting a CD-Rom2 and an Arcade Card Pro. This will allow me to play all games except for Supergrafx games right?

It should, the arcade pro covers the duo games

That's great, thanks. Any suggestions for CD-Rom games? I never owned the CD-Rom add on first time around.

hai you cannot play the super grafx games and as for the CD rom stuff...  depends, how much u can afford!?!

Gradius II
Snatcher CD-Romantic - if you dont mind wading through lots of japanese text!
Akumajō Dracula X - Rondo of Blood - kinda a prequel to Symphony of the Night - expensive !
Puyo Puyo
Puyo Puyo tsu - much more rarer and expensive
Cotton
Wonder boy III - Monster Lair
Dungeon Explorer II - try and get the USA version. cd rom games are region free
Ys Book I & II
Dragon Slayer
Gate of Thunder
Lords of Thunder
Super Raiden
Populous the promised lands
Rainbow Islands
Art of Fighting
Fatal Fury special
Nexzr
Star Parodier
Ai - cho ainiki - if you dont mind the homosexual themes
Valis III
Valis IV

Cool, thanks!

I'm not really a collector so will pass on any that are particularly expensive. Are there any price guides online?