Basilisk II works fine under Snow Leopard. You can get the latest build from
here.
SheepShaver and Mini vMac work fine also.
The most appropriate one depends on your desired usage: SheepShaver emulates a PowerPC (G3, I think), and can run System 7.5.2 up to Mac OS 9.0.4; Mini vMac emulates a Mac Plus, and can run System 1 through to System 7.5.5; Basilisk II emulates a 68k Mac and can run System 7 through to Mac OS 8.1.