A quick way to find your Steam ID is to simply log into SteamID using your steam account. On the top of the site there is a "Sign in though Steam" button. Click this
From Steam Profile Page
Load profile page on steam
Right click "Copy Page URL"
Paste into SteamID
Search
Via in game console
In generic Valve Games Enable developer console under keyboard options
Open console using `
type status
Find your name and the cosponsoring Steam ID or Steam3 ID