What system generated indexes don't start with "_WA" (although these are not really indexes, only statistics)? If you are referring to system generated primary keys then try this on sysindexes:
select name from sysindexes
substring(name,rtrim(len(name))-8,len(name)) like '[__][0-9,A-F][0-9,A-F][0-9,A-F][0-9,A-F][0-9,A-F][0-9,A-F][0-9,A-F][0-9,A-F]'
Of course this is not robost, unless all system generated names always end with a '_' followed by a 8 character hex number. Plus someone could also name there non-system generated name with this same convention.
If you are not talking about system generated primary keys then, what other indexes might you be referring too?
Gregory A. Larsen, MVP