Network mapping software

hi

I have a number of Dell PowerConnect switches (mostly 6248), along some Cisco devices spread out over two data

centres. I'm looking to create some network diagrams of two data centres and am hoping someone can recommend

a good piece of network mapping software that I can use to map out switches, routers and links.Im wondering if there is a HP Openview or 3com network director equivalent for Dell that 

I can use with read only SNMP strings.  Please advise....

thanks