Windows 95
Unofficial Windows 95 OSR2 Service Pack 1.05
OSR2SP1.EXE
Windows 98
Unofficial Windows 98 Second Edition Service Pack 3.65
U98SESP3.EXE
Windows 2000
The USP's are all fully cumulative, which means that they contain everything from Service Pack 4.
Microsoft Windows 2000 Unofficial SP 5.1.2195
usp51.zip