Safecount has a menu of invitation techniques:
"Which invitation method works best on my site and will create a more seamless experience for users?
"Which invitation method performs better?"
DHTML-based floating invitation. Avoids pop-up blockers and garners 2-5% CTR. Creative customizable.
Interstitial | Full page invitation
Link - Avoids pop-up blockers and garners 12% CTR. Creative customizable.
Jumppage - Similar to Link, this full page interstitial survey invitation loads in front of the designated recruitment page. Avoids pop-up blockers. Content and creative are customizable.
A popup survey invitation that uses existing assets on a web page to enable an invitation to every nth user upon exit of the domain of a website. Garners approximately 1.2% CTR. Note: only available for HTML