ZX-Emul is a ZX Spectrum 128k, Pentagon 128/256/512/1024k, and Scorpion ZS 256/1024k Emulator. Does a rather good job. Supports sna (both 48 and 128k), bin, rom, Z80, tap, tzx, trd, scl, fdi, and udi formats. Also has a build in debugger.