Essentially, every 20something girl should have a nice piece of jewelry, whether it is a lovely Yurman bracelet that she wears almost daily or a right hand ring. Lovely jewelry is not just for those who were engagement and wedding bands and are given jewelry on anniversaries and birthdays and Christmases.
Save and buy your own jewelry. We aren't talking about 2 Carot diamond pendants, but a nice set of pear earrings or an emerald ring is classic and dresses up both work and play outfits. You can mix nice jewelry in with knockoffs, but if you have a decent job and places to go, invest in something small that makes you feel like a million bucks.
I am in no way suggesting that you blow all your money on fancy gems, but just because your left hand doesn't sport a big diamond doesn't mean you don't deserve a little bling.
My suggestion: a set of pearl earrings, a pear neclace, or a yurman bracelet.
I probably only have 2-3 nice pieces of jewelry, but if I never get married, I plan on purchasing a piece every few years. There is no reason to end up single and fifty, wearing Target jewelry because I waited for a man to buy it from me.
(1) Check out JTV.com (jewelry tv) -- you can actually find good deals here. I'ev ordered a ring from there before.
(2) Mix in a Yurman with fakes until you can afford a few yurmans (this is what I am currently doing!)
(3) a pearl ring will give you the most bang for your buck. You can find a decent one for under 200 and its class enough to wear to job interviews but glitzy enough to wear to a cocktail party
(4) If you are not a jewelry person, don't invest tons in jewelry, but have the few key pieces you can wear for years -- pearls, a nice ring, diamond stud earrings, etc.