Dont have a wheel or control pad, that don't matter really can play on keyboard.
Really

Seriously treat yourself to an XBox 360 pad, they're not exactly wallet busting
At least then you've got some sort of analogue control, rather than full lock left/full lock right.
just want to know the best racing games with the best graphics, hopefully with some kind of campaign/career mode.
Unfortunately best graphics doesn't necessarily mean best game, so you kinda' need to make your mind up what you want?
Having said that Dirt 2 and F1 2010 may be right up your street. Both have decent graphics, and they also feel fairly good in the handling stakes, albeit slightly arcadey.
They both have pretty good single player career modes though, and these games would be a good choice I feel, especially if you're more of a casual racer.
Shift 2 for me is a bit of a letdown, although I play on the wheel and one of my mates seems to cope fairly well on his 360 pad.
It all just feels a bit vague, floaty and laggy no matter how I set it up.
If you want a sim then iRacing always gets positive feedback, although you do have to pay a monthly subscription.
I can't comment myself as I've never tried it. Not sure iRacing has a single player mode as such, perhaps someone who plays it can chime in and let us know?
GTR2/Race on - along with its many add on packs is also a great sim,
brilliant with the wheel but unfortunately the graphics are starting to look a bit dated now, although there's loads of mods to be had that can enhance it.
RFactor is another good sim, but again dated graphics. RFactor 2 should hopefully be out sometime this year though.
Dirt 3 is also out at the end of this month, this looks really promising graphics wise, of course we'll have to wait and see how it handles, but initial reports seem good.
There's plenty of older games that still look pretty good graphically, both Toca Race driver and Grid are good games to play and both come complete with Codemasters rather arcadey but generally positive handling.