I am in the middle of Heartgold on my DS and want to know the easiest and fastest way to evolve my Togepi. He is already holding the soothing bell item.
Visiting the Haircut Brothers in Goldenrod tunnel will provide a small boost to happiness once per day.
Daisy is also available in Pallet Town from 15:00 to 16:00 for another small daily boost.
A third option is to make him fight. Leveling up provides a friendship boost, assuming you don't faint, of course. Fighting Gym Leaders and Elite 4 members will also provide a boost, independently of leveling up.
You could also try the following berries :
- Grepa (SpeDef)
- Hondew (SpeAtt)
- Kelpsy (Attack)
- Pomeg (HP)
- Qualot (Defense)
- Tamato (Speed)
Those berries will raise the friendship of the Pokemon by a small amount, but will also decrease the EVs of the corresponding stat by 10, which may help if you're EV training and made a mistake. Note that these berries cannot be used if the Pokemon has 0 EVs in their corresponding skill.
Edit : A fifth option, although fairly expensive, is to give Vitamins to your Pokemon. THose will also provide a small boost, as well as 10 EVs for a stat.
Worth noting that walking around also passively increases Friendship.