Check out this awesome pokedex:
Also, because it's a happiness evolution, read this fantastic jewel of info by Frost
Try the vitamins and berries, but also train him in battles (level it up) , walk around with him a while, don't let it faint, feed it pokeblocks, give it a soothe bell, and try using it against the E4.
Hope it helped!
EDIT: Sorry I presumed you hadn't done your research. Edited the post, and BTW, this was the way I got my Eevee to evolve into Espeon and my Golbat to evolve, so I'm glad it worked for you. Sorry again.
Awesome Siggy: Spongedude
Fantastic Avie: froggy_00 If I owe/ said I would donate you psybucks, please PM me ASAP (preferably a link to the page that I "bought" the item) and I will try to round them up as quickly as possible (of course, after the cash mod is fully functional). Thanks.