ReCaptcha can be one of the most annoying captchas out there. Are there alternative captcha solutions out there for native civi profiles and pages?
I like CiviHoneypot myself, especially on contribution pages.
Not quite a captcha solution but this extension blocks repeated submissions on a contribution form from the same IP address. https://github.com/fuzionnz/nz.co.fuzion.iprestrictions
This wouldn't prevent the use of Tor or similar to mask ip addresses, and doesn't currently work on profiles.