The Orange Pippin is a good starting point, if not so thorough and complete as one might like.

Here is a link that might be useful: Orange Pippin

I use Century Farm Orchards, Cummin's Nursery and the Master Variety list on Big Horse Creek Farm's websites, they are all pretty good. Cummin's Nursery being the most thorough and scientific.

If you want more data about apples, the ARS GRIN is a good source. It still won't give you everything you are looking for and it doesn't have all the newest apples, but it has a ton of old ones. Brix is listed as "Solsolids".

Here is a link that might be useful: ARS GRIN's apple page

Wow. Thanks.

Others, keep adding.

I ran into Orange Pippin, and submitted a bunch of what little I knew about a bunch of Canadian Prairie varieties.

The ARS GRIN page is amazing at first look, although very dense. It will take me a while to learn how to use it, and mine what I need out of it. It has some hardy apples, notably battleford and goodland, honeycrisp, norland, dolgo, rescue, kerr.

It's missing others: Gemini, norkent, odyssey, prairie magic, red sparkle, september ruby, winter cheeks.

For people coming after me:

Century Farm Orchards
Fairly short list (3 pages) of, I'm guessing, zone 5+ varieties.
http://www.centuryfarmorchards.com/descripts/osadescripts.html

Big Horse Creek Farm.
300 plus varieties, most with a picture of the fruit (and their are some weird ones). Has some colder zone apples, but not quite to prairie cold. Under resources on this page there is a bibliography of books, (many out of print) and a page of links elsewhere. Recommended.

http://bighorsecreekfarm.com/

Cummins
Good New York grower. Good information on the varieties they have but not an earth shaking list.

http://cumminsnursery.com/

Kerr crab(DolgoXHaralson) - small - 1.5-2.0" fruit. red skin over crisp, firm, tart white flesh, with musky wine flavor undertones. A fave here, for 15 years or more.

Paired with its half-sib, Centennial (DolgoXWealthy), which is a bit larger, and sweeter... it's a hard combination to beat.