Uh, this is way back in Silver the Original, but mainly I just ran around in the grass outside Mount Silver and levelled up there. Also, going back to places and catching pokémon I hadn't got on my first go through, and running around after the legendaries, but obviously that's even slower. Less boring, though. (I am a person who enjoys levelling, though, so maybe it wouldn't work for you.) [EDIT] Also Victory Road is usually pretty good, for pokémon who don't make faces at rock/ground/steel types, which mine usually do. ^^; [/EDIT]

Usually going through the Elite Four works pretty well, too. Maybe have some sort of arbitrary challenge to keep you interested? Seeing if you can beat them all without healing/with just one pokémon, etc. etc. (Or with an exp. share on something lower levelled you just want to evolve for your 'dex, but again, that's gonna be slower.)

Rare candies don't give you the EV points, which are super confusing to me, but basically you're not as strong when you level up with rare candies as opposed to normal levelling, so I wouldn't recommend it. (Also getting that many rare candies is probably gonna take as much or more time as just levelling, so, you know. =/)