I've never had problems with the old Lucent 1646T00 modems, they worked on nearly everything (even 486's), were stable at nearly any bus speed (other cards would fail first), and cost around $10. They're no longer produced as far as I know.
<font color=blue>Only a place as big as the internet could be home to a hero as big as Crashman!</font color=blue>
<font color=red>Only a place as big as the internet could be home to an ego as large as Crashman's!</font color=red>