Great CCW guns: Walther P99 .40, Kimber .45
Good gun really cheap: Makarov 9x18
You'll get 10,000 opinions on this and most of them are valid. But ignore the ".45 caliber only" bunch. It's a great caliber, but the notion that its the only caliber on earth is emotion-based. Many others will do a fine job including .44, .357, 9mm +P, .38 +P, .40 and more. Even the mouse guns have their place, and any bad guy who doesn't take a .380 or .32 seriously is a genuine idiot.
And please, I beg you... don't become a police officer. PLEASE. We need people fighting for liberty, not against it.