Software I frequently use (as my games are written on the Speccy directly):
Laser Genius (1986, Ocean Software), HiSoft Devpac (1983, HiSoft), The Artist (1985, Softechnics), User Defined Graphics (1982, Oxford Comp. Publ.), Zeus Assembler (1983, Crystal Comp.), 3D Construction Kit (1991, Domark Ltd.)