Ooh, has someone ported an emulator?
Exile
2d action adventure with a strong physics slant. Later ported to Amiga.
Chuckie Egg
Just like the Spectrum version, but with slightly different physics, and the bird doesn't kill you while still caged.
Vortex
Into-the-screen 3D shooter. Pretty cool for its day.
Frak!
Stupidly hard platformer. Worth playing for the music, and a protagonist who swears when he dies.
Imogen
Thoroughly charming platforming puzzler. A Windows port was made a few years ago, but I prefer the monochrome look of the original.
Thrust
Physics-based shooter. Also ported to other systems, but IMO it works best on the Beeb.
There's plenty of other games which are decent ports of arcade games, or games from other platforms that you can already play on Pandora. Planetoid is worth playing still - it's a slightly more forgiving Defender clone, and looks (and sounds) the biz.