Chaos Field, Radilgy, and Karous are on Ultimate Shooting Collection for the Wii. That runs about $20, and they're in English, so importing those for the Dreamcast is overkill. Trizeal has a (Japanese) PS2 port that costs a lot less. Ikaruga was on the Gamecube in English and is hard to find and expensive, but nowhere near as hard to find or as expensive as the DC version. I believe Border Down and Under Defeat are actually Dreamcast exclusives.
Shenmue II was on the original Xbox, but the Xbox version is dubbed, and you can't port your Shenmue 1 save (although porting it for the DC takes some trickery--editing the save file to add the European flag is easy, but getting it off and onto the DC is hard. Too bad nobody has written a homebrew disk to modify the save file in place.)
