Just an interesting list I compiled after looking at many hosts and doing some research:

HostGator
4871 of alexa:
http://www.alexa.com/data/details/?url=hostgator.com
31,067 domains:
http://www.webhosting.info/webhosts...s/HOSTGATOR.COM

LunarPages
2176 on alexa:
http://www.alexa.com/data/details/?url=lunarpages.com
domains: doesn't seem to load... i will update this when it does.

Powweb
2770 on alexa:
http://www.alexa.com/data/details/?url=powweb.com
84,062 domains:
http://www.webhosting.info/webhosts...ains/POWWEB.COM

Netfirms
868 on alexa:
http://www.alexa.com/data/details/?url=netfirms.com
87184 domains:
http://www.webhosting.info/webhosts...ns/NETFIRMS.COM

BTW, for those of you who aren't aware of webhosting.info, it has a great service... you can check specific information on hosts such as how many domains they own, their growth etc.

Does anyone know of any other large hosting services?

this can be really handy for ppl that are looking for hosts and wants some info about the hosting company etc.. great find!

I found another really big one: http://www.webhosting.info/webhosts/.../DREAMHOST.COM
152,397 domains.

how do they get that many people?? how much money do they get?i have never seen sites with so many people !!

I'm looking for a host for my new upcoming site and I saw some intresting things so thanks! are they all trustworthy?

I think Site5 must be a pretty big host.. and of course the free hosts that 'newbies' still use (geocities, for example)