For payroll ? We (rsync.net) have always had our payroll done by our private accounting firm. There are tons of providers - small and large - to whom you can outsource your payroll ...
Also, for the sake of completeness, you can do it yourself ...
And your accounting firm is likely using Intuit so...
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-payroll provider
+accounting firm
Gusto's a great option (I'm a bit biased, having worked there for like 5 years).