I advise against getting super-high rings. In order to get the correct height over rail, you'll need very high rings. That makes them less sturdy or rugged as a result. Unless you spend around $140 or more and buy heavy duty all steel tactical rings.
Getting a rail riser has a big advantage, in that it allows you to use regular rings. The biggest advantage is that it brings up the entire range of heights for a given ring set. So, you can buy low, mediums, high or extra highs depending on what you like because the riser rail gets them in the ball park height-wise.
For example, Leupold high rings are too short for an AR. Burris high rings are way too short. No ring set is the same as others as there's no standard determining what is high, med, low.
A riser helps a lot.
A good riser, for a good price that is solid is the Yankee Hill one piece:
Third item down:
http://www.yankeehillmachine.com/store/rails.html
There's also this rail riser that also moves the scope forward if your scope has good eye relief (like 3" or more) ...
RRA
You can buy 2-piece risers too. ARMS makes one piece risers, as do a lot of others, but these are 2 good ones that are inexpensive, yet solid.
If your scope has 30mm tube, you can buy tactical rings which would do the job. They look like this:
