I’m based in the UK, so look at low-cost European companies such as Leaseweb, Redstation, Hetzner, Rapidswitch etc
If you are in the US there are loads of dedicated server hosts there - I would look at reviews on webhostingtalk.com as I haven’t used a US host myself for a while now, but I know there are lots of low-cost suppliers as bandwidth in the US is cheap.
It really depends on your budget when deciding on what to go for, more usually means better service not necessarily better/bigger server.
In terms of OS - I would use CentOS as it has been rock solid for me for the last 7 years. If hosting multiple sites/email etc, use a control panel such as Webmin - it will make your life much easier 
