The Payment
Paying with credit cards is a good idea because it leaves a paper trail. In case something goes wrong, (e.g. a scammer sold you a fake and ran away) at least you can try to dispute the charge with your bank. Some gold or platinum cards offer Purchase Security and Extended Warranty Insurance that may cover damages or fraud. (Check with your bank / credit card company).
Some of the more reputable online jewelers, like ICE.com
, offer an "Easy Monthly Payments" program with no finance charge. Others like 
Diamond.com offer "Do Not Pay Until 2006" or similar campaigns. These offers could be helpful because the moment you want to propose might not necessarily be the same moment you have a stash of cash sitting around. Make sure you read all the fine prints before you buy. And, if a payment program is charging you an 18% finance charge, or if you think you'll carry the balance on your credit card for a while, you should look into applying for / expanding a line of credit from your bank. Personal credit lines usually charge a much lower interest rate. You can then pay the credit card in full first by borrowing from the cheaper-interest line of credit.
The Design
After you chose a diamond, you will have to choose a ring setting. Ring settings are usually made of yellow gold, white gold, or platinum. Platinum is a rarer metal than gold and therefore more expensive, but it's also a harder metal. Keep in mind that using yellow gold on the ring might cause your diamond to appear a bit more yellow (hence a lower colour grade) than it actually is.
Solitaire
(photo courtesy of Szul, Jewelry Online.
)
As for the style, the Solitaire style is a very common style. There are no side stones and so the visual focus is drawn onto just the centre diamond. For round diamonds, the settings usually have 4 prongs or 6 prongs. 6-prongs hold the diamond more securely, but 4-prongs don't block the view as much and make the diamond look bigger. You need to be careful with a 4-prongs setting because problems with one single prong can already make you lose the diamond. Ask your jeweler of what material the prongs are made; sometimes even on gold settings they would offer prongs made of platinum, because of sturdiness.
Diamond Accent Settings
Besides the Solitaire, another main category design is "Diamond Accent Settings". In the ring setting, there are small diamonds around the main diamond as accents (side stones). The accent diamonds are named by their shapes, such as baguettes (rectangular) or trilliants (triangular).
(centre diamond with two baguettes)(photo courtesy of ICE.com)
One popular design is called "Past, Present, Future", with one centre diamond and two side diamonds, representing past, present, and future.
(photo courtesy of Diamonds International
)
Bridal Sets
(photo courtesy of Blue Nile
)
Bridal sets, or wedding sets, are sets of two rings: the engagement ring and the wedding band. They have matching styles, and are designed to fit together to be worn on the same finger.
We have also seen 3-parts wedding sets: with 2 wedding bands sandwiching the engagement ring in the middle.
There are indeed many different styles, probably too many. To help you get some better ideas, you can see what's recently purchased by others at Mondera.com's "Recently Purchased Engagement Rings
" section. You should also visit our "Interviews with the jewelers" section and see what they say about the latest trends about wedding band and engagement ring designs.
