My favorite is RCT3 - Platinum. I see it's for sale on Amazon for about $15 and I know you can find it at either WalMart or Target for about $20 since I bought a backup copy of it about 6 months ago. The fact that you can still find it for sale in stores some 7+ years after it came out is is kind of amazing but it was such a good game that it keeps selling. It has yet to be surpassed as the all-in-one package for roller coaster gaming IMHO. ( meaning you can find games that let you build a coaster only but not much of a park, you can find games that let you build a park but not too much along the lines of coaster design. )
I built Disneyland in RCT1 back in '99 ( and got linked to Disney's Disney.go.com site back in the day ) and currently am 95% done building all of Disneyland in RCT3. I can't give accolades to this park/coaster builder nearly enough. I'd recommend it and the price is more than fair.
For a sim? I wouldn't think so but I should openly admit that I like the game enough I might not be an impartial source. Once you're in the first-person ride mode it looks great. When you're back to the top-down-3/4-view mode the graphics are about as best as can be expected. Honestly, my Win 7 64-bit comp with only 4GB of RAM and a newish 512MB video card sometimes has trouble running it unless I set the graphic levels on the video card down nice and low. I've never seen how good it could look at it's best with a top-notch video card and 12GB or more of RAM.
Here's a decent screencap of what someone else did. It's enough to convey an example.