Diamonds, like the love they represent, are unchanging -- the hardest stuff you'll find not designed by NASA. What has shifted, when it comes to the engagement rings they often adorn, is how they're bought. Old-school etiquette said that a guy surprised his girlfriend with something he'd picked himself or maybe inherited from Grandma.

These days, a woman can have plenty of input, whether by opening a magazine to a certain page and placing it just so in a well-seen spot (hint: try under the remote) or by outright volunteering to go shopping. Not that there's anything wrong with that. After all, says manners maven Peter Post, "You want to make sure it's the ring you want."

The ones on these pages might tempt even the most traditional bride-to-be to take matters -- and jewelry trays -- into her own hands. In tons of shapes and styles, these rings share one dazzling trait: the ability to take your breath away. Sparkling emerald cuts, ovals framed by side stones, pave bands, and even candy-colored solitaires -- each seems more brilliant than the next, proving that the only thing harder than a diamond (or a tourmaline, perhaps) is picking the one you'll wear forever.

Top (clockwise from top): Kwiat; De Beers; Tiffany & Co.; Harry Winston; Ritani; Kirk Kara (top), A. Jaffee; Michael C. Fina; Rina Limor Designs; Hearts on Fire (top), Tacori; Hearts on Fire; Ritani (top), Kwiat.

Best New Bands
If a doorknob-size rock isn't your style, think about swapping it for a diamond-studded band. Razor-thin pave styles, eternity bands of channel-set chunks, delicate floral motifs -- the choices are more varied than you might think. You can choose to keep it solo once you're wed or stack another band on top. Bonus: A circle of smaller diamonds with the same total carat weight as a solitaire can cost lots less than the single stone -- and can be just as pretty.

Left stack from top: Kirk Kara, OGI, Ritani, OGI, Rina Limor Designs, Furrer-Jacot, Penny Preville, A. Link. Right stack from top: Gumuchian, Peter Storm.

A Boxful of Eye Candy
What you settle on is a matter of taste (and budget). You might crave a prong-held solitaire or flashing sand-fine pave diamonds. Or maybe a ring with streamlined, Art Deco-like side stones is more your style.

First row: Tacori. Second row, from left: Kirk Kara; Christopher Designs. Third row, from left: Rina Limor Designs; Stephen Russell; Tacori; Kwiat; Tiffany & Co. Fourth row, from left: Christopher Designs; Tiffany & Co.; De Beers; Penny Preville. Fifth row, from left: Bulgari; Cartier; Kwiat; Christopher Designs; Chad Allison. Sixth row, from left: Stephen Russell; Christopher Designs; Rina Limor Designs; Ritani. Seventh row, from left: Hearts on Fire; Harry Winston; De Beers.

Rock Stars
Do you love the look of a large stone but can't bring in the bling under budget? Why not go with a ring that's set with a colored semi-precious gemstone instead? Cool blue aquamarines, pretty pink tourmalines, a hunk of honey quartz in cocktail-ring dimensions -- all make a bold, brightly hued statement and deliver an of-the-moment look that's all yours. Its definitely a trend that's big in every way but the price tag.

Clockwise from top: Padparadsha sapphire from Fred Leighton, pink tourmaline by Verdura, aquamarine from Fred Leighton, honey quartz by Mish New York.

How the Choices Shape Up
Although round diamonds still reign as the top pick with brides (nearly half of all engagement rings sold feature this stone), the range of popular alt-rocks keeps growing, from rectangular emerald cuts and vintage-looking cushions (they really do look like overstuffed pillows) to fiery, flashy princess cuts, fit for, well, you guessed it.

Top: Fortunoff. Second row, from left: De Beers, Fortunoff, Cartier. Third row: Cartier, Tiffany & Co., De Beers (2). Fourth row: Tiffany & Co., Cartier, De Beers.

Dazzling Diamonds

A sparkling array of stunning diamond rings.

Top, from left: De Beers, Hearts on Fire. Second row, from left: Tiffany & Co., Stephen Russell, Ritani, Cartier. Third row, from left: Harry Winston, Diana Classic, Christopher Designs, Bulgari. Fourth row, from left: Michael Beaudry, Fred Leighton, Michael C. Fina.