You can solo BC 25 and WOTLK 10 raids in epic gear, but these have WEEKLY RESET.
RAIDS:
Black Temple
1 hour
570 gold
600 Netherweave Cloth (AH price: ~50 gold per 200 stack)
Serpentshrine Cavern
30 mins
300 gold
50 Netherweave Cloth
Karazhan
50 mins
400 gold
150 Netherweave Cloth
Sunwell Plateau
45 mins
500 gold
100 Netherweave Cloth
Naxxramas
1 hour
900 gold
Frostweave Cloth (AH price: ~200 gold per 200 stack)
There are several short raids, like:
Magtheridon's Lair
3 mins
30 gold
Gruul's Lair
4 mins
40 gold
Crusaders' Coliseum
15 mins
190 gold
The Nexus
3 mins
50 gold
The Obsidian Sanctum
less then 5 mins
100 gold
The Ruby Sanctum
7 mins
90 gold
etc.
Some raids are annoying, like: Ulduar, Onyxia's Lair.
You can't solo CATA raids! If you have 500+ gear, maybe you can kill the thrash mobs only, but not the bosses.
DUNGEONS are repeatable, 10 runs per hour is the limit. Here is some:
Lost City of the Tol'vir CATA
6-7 mins
90-100 gold
repeatable: 1 hour ~ 900 gold
Gundrak WOTLK
5 mins
50-70 gold
repeatable: 1 hour ~ 600 gold
Only heroic dungeons of BC are even effective, but these have 1 hour reset. Completing them in turn, could be a good strategy, but requires lots of traveling.
PETS:
Pets drop in RAIDS, but if you think you can sell them for 5k each, you are wrong. If you are lucky, you will get 1500-3000 for a new pet. The price of the old pets between 10 and 300 gold. Most of the time other players will undercut you, and your auction will be expired. You will be forced to lower the price.
PROFESSIONS:
Production professions are completely useless at 90, forget them. For example, jewelcrafting: you can create rings, necklaces, trinkets, gems. All trash. Nobody will buy anything from you. Maybe if you put these on AH for 1-2 gold.
Usually this doesn't help either. Only collecting professions profitable: skinning, herbalism and mining.
Collecting materials requires a fast flying mount (neither riding skills nor flying licenses are cheap). Not all materials are in demand: for example Fel Iron Ore is always sellable, but Adamantite Ore isn't. Cobalt ore is always sellable, but Saronite Ore isn't.
Collecting 200 minerals takes around 45-60 mins. The leveling materials are the important ones.
Fel Iron Ore, Cobalt Ore: 1200-1500 gold (always sell)
Adamantite Ore, Saronite Ore: 600-800 gold (barely sell)
Obsidium Ore: 1000-1200 gold (always sells)
Elementium Ore 800-1000 gold (sometimes sell)
Ghost Iron Ore 150-300 gold (there are too many in AH)