For you, for this one, I'm open to a "one off" - since I've never come across a well known / well regarded "domain leasing" site.
Frankly, I suspect such a website would be a miserable failure, unless it was a small sub-domain of a much larger/successful domain aftermarket site. (I'm not even a big fan of the aftermarket sites as the may tend to feed the perception that simply listing crummy domains may lead to sales. It doesn't happen that way, as evidenced by the tiny fraction of listed domains that actually sell.)
So, anyone want to spam . . err, suggest . . a domain leasing site? :P
P.S. It's hard enough to sell a marginal domain. Leasing one, where the lessee does all the work to add value, is rarely a sound business plan for future success . . unless the leased domain is held in escrow by a trusted third-party during development + specific written lease + . . .
My $.02 - No lease. Lease purchase with Escrow and well defined contract terms, including definition of "damaging the domain" so the lease can be broken for spammy/blackhat behavior, etc.