Oooh... my first post here!
Lens cleaning is a topic of some debate in the photographic community. I'll try to qualify what I know for certain vs. what I think.
As blacknet points out, cheaper lenses will have far less durability in cleaning either due to lower quality multicoating on the lens, and lower quality construction, though plastic in the optical portion of a lens is a rarity in SLR lenses, though quite common in point and shoot cameras.
One thing you should do is clean the lens in concentric circles starting from the outer edge and working towards the center.
Microfiber lens cloths are the best. Avoid lens paper if you can, though its better than a shirt, which you should not use. NEVER use toilet paper, kleenex, or paper towels. Try and use a compressed gas airduster or a camelhairbrushblower to clean the lens first. If this doesn't work or if there is smudging, I usually try just breathing on the lens and cleaning with a microfiber lens cloth, which I will moisten with water if necessary. Only when the lens has serious oil do i use a cleaning solution. You should apply the solution to the cloth rather than directly to the lens. Always use the airblower/brush first before wiping to prevent dust from being rubbed around and scratching the coating.
The anti-reflective (AR) coating is usually what gets scratched, rarely the glass (although if you have plastic that will scratch easily, as blacknet already noted).
Conventional wisdom says don't over clean your lens. Don't clean when it's not necessary. AR coatings are much more durable than when they first appeared, but you do hear stories about people who clean their lenses daily and end up with the coating scratched or coming off over time.
I would probably buy a photographic lens cleaner rather than one from a shop (I can't remember, but i think the trick is to remember to avoid anything with ammonia in it, but I might have that backwards), although the really good one that Sunglass Hut might be OK (i dont know) because its used on Oakleys, which have really weak coating, but that's for looks, not AR, so the fluid might hurt lens AR coatings. RoR is a popular lens cleaner and gets rave reviews. I used it several times but found it always left streaks.
If you want the best microfiber cloths ever, buy a Microdear cloth (it's so popular in Europe and was so requested in the USA, that Adorama specially imports them):
http://www.adorama.com/catalog.tpl?op=details&sid=103869598926035234&sku=CPCML
http://www.adorama.com/catalog.tpl?op=details&sid=103869598926035234&sku=CPCMS
I have one and I can tell you they are worlds better than the $6 at the local camera shop. So buy a filter or some film from Adorama and have a lens cloth thrown in. Caveat on film orders from Adorama: they sent me short dated film, though they agreed to take it back.
