I think I booked the biggest win of my life in the $15/$30 limit Omaha game in NOLA. I think I erred in the description, too... the $15/$30 is exclusively Omaha high, while the $4/$8 games are half/half.
re: Blackhawk, either the Lodge or the Ameristar (more likely) will have the $10/20 and $20/$40 limit games. They are right across the street from each other. I actually like playing at the Golden Gates over the Ameristar or Lodge. For the games you are looking for, those are the three main cardrooms. I've never seen any limit games at the Gates above $4/$8.
The gaming laws in CO restrict the max bet to $100, so the "no limit" games are really "spread limit" i.e. $1/$2-$100 NLHE has $1/$2 blinds, with a max bet of $100. Max buy-in might be in the $300-$500 range for a game like that.
It doesn't matter where you stay in BH, as all of the casinos are within easy walking distance of each other. Hell, some of them even have bridges between them. You might be able to get some reasonable rooms at the Isle of Capris. I stayed there once, and the decor on my floor was this ghastly green tropical theme, but the room was standard (think Super 8). I just did a spot check, and it looks like the Isle has weekend rooms for $129 for most of April.
There are no commercial chain hotels like Holiday Inn, Hampton, etc. anywhere close to Blackhawk/Central City.
Also see:
http://www.coloradogamingnews.com/
http://www.blackhawkcolorado.com/
Lastly - if you are coming over from Chicago, I would definitely stop in Council Bluffs on your way over to Denver. CB is almost EXACTLY halfway on what Yahoo! Maps tells me is a 14.5 hour drive. There are a bunch of cheap/budget hotels near the casinos in Council Bluffs.