Understanding the motivations for the 21 million BC limit and halving reward rate, I still think it dis-proportionally rewards early adopters. My ideal system would be one where the mining reward is a factor of the work done which would mean as the system increases in popularity (i.e more miners) the corresponding mining reward would increase. This would have a stabilising effect on the price and provide people a reason to spend coins rather than hoard them. Anyone who has tried to work or sell goods in BC's would see the problems it is facing as a currency rather than a commodity. Does anyone know of a Bitcoin alternative with these properties?
PPCoin appears to have a non-reducing block reward, so that might be what you're looking for.
Other alternative cryptocurrencies are listed, with some info on their properties, here: https://en.bitcoin.it/wiki/List_of_alternative_cryptocurrencies
Freicoin also accomplishes this but in a round about way. Rather than adding new coins to the system to pay miners, it removes coins from each account to pay miners.