Ubersmith Owned License - 100% owned with no monthly fees
We recently swapped our license out for an unlimited so our owned 250 Client ubersmith license is up for sale. You cannot buy these any longer direct from ubersmith.
Its a Ubersmith Owned Pro 250 license however since Pro has been discontinued according to ubersmith support these will automatically be upgraded to DE licenses as of May 1st 2011. It qualifies for support with ubersmith which is currently ~15/month but will be going up to 49.95/month and a steal for the fantastic support they offer.
Check out http://www.ubersmith.com for a complete feature list and api guide. This is by far the best all around billing system on the market and most extensible you can find.
Please be realistic with your offers and make them via PM.