Devil's Crush and Alien Crush are two essentials. They aren't expensive, are great games, and really work great on the GT/Express.
Wait, I'd say although both good, if you're building up a library on the cheap, you don't need both - and I'd go for Devil's Crush every time.
I had my GT for years with 8 games, and there's a thread I started on here last year about portable gaming. Let me have a bit of a think...
Sonson II as mentioned in the capcom thread is a great, deep game with big sprites that works well.
Any of the P
C Genjin games are great too, I'd probably go for 2, others would certainly disagree.
Be-ball is a fun little puzzler that can be picked up on the cheap, and has big easy to see sprites
Puzznic is also great, but suffers a little with the code input hard to see on the screen. But well worth it.
As far as shooters go, you need to be careful with bullet sizes. It's been a while, as I tend to play shooters on the big screen, but I think
Cyber Core works well, and the
soldier series should be good too. Someone correct me if I'm wrong here.
It's real sad
Daimakaimura is non portable, that would go great I think.
Shubibinman 1 or 2 should be pretty good for some Megaman-ish action
Altered Beast does work, but I don't happen to think it's that great.
Motoroader works fantastically, but obviously you don't get the multiplayer
Same as above for
BombermanShinobi is cracking good fun, IMO, and if you can get around the horrific scarabs, it's hours of fun.
Surprisingly,
Street Fighter II works pretty good, despite the lack of buttons. But it won't ever feel quite right.
Mr Heli works pretty well actually.
Parasol Stars, didn't spend a lot of time playing it on the GT, but it seemed perfectly playable.
errm..I think... that's enough to be going on with. There's probably a few more in my collection that I'd pack in the case, but I can't really think of any more right now.
Afterburner II maybe, but it's pretty dated.
What am I saying! Forgot one of the best shooters on the Engine, which works great on the GT!
PC Denjin, AKA
Air Zonk!
Can I think of any more.... Oh
Jackie Chan maybe?