I probably shouldn't do this, but as with other things in life that one shouldn't do, I'm gonna go on and do it anyway!
I'm going to give you some tips on rare spawns in Vanilla that have high chances to drop blues and that could earn you some extra cash. All the rares in Outlands and Northrend drop blues, but only very few of the Vanilla ones do. And most of those blues are rather good and will therefore give you some 30-100g on AH. Here are my top three favorite rares in Vanilla.
Lo'Grosh is an ogre inside one of the ogre caves in Alterac Mountains. He has a good chance to drop not only one, but two good blue items. Black Ogre Kickers, really nice level 32 mail boots with strength and stamina, and The Pacifier, an awesome level 32 mace (4.00 speed!) with tons of strength and some stamina. Both these items are worth more than 50g at AH. Lo'Grosh himself is level 39, so when you quest in these areas he should be around your level. He isn't elite either but hits rather hard and uses bloodlust which will make him hit even harder.
Yet another npc situated in Alterac Mountains. This is nice because you can just run to check if either is up any time you're in the vicinity. Skhowl is a yeti just behind the goblin Bro'kin that sells the Frost Oil recipe. Skhowl is the only black yeti among all the white yetis, so he can't really be missed. He drops a really nice level 31 dagger, Howling Blade, which one can get about 20-40g for depending on server. Skhowl is killed more often than Lo'grosh and therefore the prevalence of other Howling Blades on AH is usually greater than with other boe blues. Skhowl is level 36, also non-elite and really easily killed.
3. Ironeye the Invincible
Ironeye wanders the southern parts of Shimmering Flats, and really stands out in the white sand as he is an all dark greenish basilisk among all the white basilisks. Ironeye isn't easy at all, he is level 37 which is rather high for that area and also elite which makes him quite tough for anyone around that level to kill. He has a high chance to drop Blade of the Basilisk, a really cool level 32 sword which has a chance on hit to increase defense by 50 (!) for 5 seconds. At that level, 50 defense is tons, giving the wielder a big amount of dodge, parry and crit reduction for a short amount of time. Although it gives defense, this weapon is good for rogues and dps warrior as well and you could probably get more than 50g for it at AH. As with any vanilla weapon however, this probably has a low proc chance. The weapon has a really rare skin too which I might talk more about in another post.
Do you know of any other rares that drop good blues?
Good luck hunting!