IP address space management

We are in need of a software package to manage our IP space. We've looked at
several products on the market but haven't found anything that really suits an
ISP's needs very well. Does anyone know of anything on the market that works
well? It should understand CIDR and be hierarchical. Most products we've seen
have been aimed more at the Enterprise market and include a lot of things we
don't need like interfaces to DNS and DHCP. Any suggestions?