Definitely. I have been an advocate for class variants ever since I read p.94 of the 3.0 PHB and, in general, prefer them (and an occasional new base class) to PrCs.
In addition to the following non-core classes :the Psychic (Green Ronin), the Shaman (Green Ronin), the Witch (Green Ronin), the Knight (Hong's adaptation of the OA Samurai), the Swashbuckler, OA Shaman, and the Myrmidon (AEG), my campaign use the following changes and variants.
1. Barbarian:
variants: Hunter (UA), Urban (my own).
By combining the Hunter variant with Favored Environment (UA) and Weapon Groups (UA), I have created a number of cultural variants.
2. Bard:
Skill list: Concentration, Diplomacy, Craft, Knowledge, Listen, Perform, Profession, Speak Language, Spellcraft, Use Magic Device + additional skills by variant
Spells: can cast charm + illusion spells from bard list. Additional spells based on type of variant.
variants:
Bardic Sage(UA), Divine (UA), Savage (UA), Skald, Troubador
3. Cleric
hit die=d6
Good Save= Will
BAB=Poor
Armor Proficiency=Light
Spell lists are more specialized and deity specific
Divine Grace as Paladin
Spontaneous divine casting (UA)
variants: Champion of Good (UA), Cloistered Cleric (UA)
4. Druid:
hit die=d6
Good Save=Will
BAB= Poor
Must use Shapechange variant from PHB2
variant: Ollave (my True Druid)
5. Fighter:
variants: Thug (UA), several other house variants
6. Monk: when used must take Fighting Style (UA)
7. Paladin: Replaced by Champion of Good (UA cleric variant) and Spellless
8. Ranger: replaced by Hunter (UA barbarian variant), Wilderness Rogue (UA variant) and spellless.
9.Rogue:
Variants: Martial (UA), Wilderness Rogue (UA which replaces my original)
10. Sorcerer:
Diplomacy, Intimidate and UMD are class skills
Eschew Materials at 1st level
Bonus metamagic feat at 5th level and every additional levels
variant: Battle Sorcerer(UA)
11. Wizard:
speak language is a class skills
12. Wizard Specialist
Must use the Specialist Wizard variant abilities (UA)
13 OA Shaman
variant abilities