I don't think you need to buy a floating card effect as such, I think you just need a hook up for your IT that's comfortable for you and achieves the desired result. I'd thoroughly recommend getting hold of any books or DVDs on IT, as hookups will probably be covered, and you'll have a few ideas to make the floating/whirling/hummer/UFO/whatever card more your own.
I reviewed
Michael Ammar's Easy To Master Thread Miracles Vol 1(see permanent wallet hookup), and I understand that the rest of the series are just as good. Also it might be worth reading LeClair's 'Who's afraid of IT?'.
If it's as a finisher to Nailed, then just a simple, single, semi-rise to your hand will probably be the knockout punch at the end of the effect that the audience need.
I don't like the fact that the hummer/whirling/floating/whatever card is sold separately - it's on IT DVDs that may cost over twice the price, but you get five times as many effects and enough tips to last a lifetime!
Thinking about it, how about a watch hookup? PM me if you don't get it.