Bar Refaeli & Leonardo DiCaprio

Bar Refaeli & Leonardo DiCaprio has been together since 2005, and while engagement rumors are often flying, they haven't made any moves to tie the knot. It doesn't help their plight that Leo has a history of what Sex and the City introduced as "modelizing": a phenomenon that occurs when a person exclusively dates models. Kristen Zang and Gisele Bundchen are among his exes. Bar Refaeli was also linked to Baywatch actor David Charvet.

Rebecca Romijn & Jerry O'Connell

Rebecca and Jerry have been together since 2005 and married since 2007, and Romijn gave birth to twin girls in December. Considering there's only one Hollywood romance in their past (remember when Rebecca was married to John Stamos?), these two have a good chance at survival.

Salma Hayek & Francois-Henri Pinault

Salma and Francois-Henri have been together for a couple of years, and they have a baby girl named Valentina. Salma is no stranger to high-profile relationships, having dated Edward Norton and Josh Lucas before tying the knot with Pinault (twice). Salma is Francois-Henri's first celeb romance, but he has two children from a previous marriage that ended in 2004. We hope it works out, but we're not making any bets on these two for now.

Jessica Simpson & Tony Romo

Tony and Jessica have been together since 2007, but breakup rumors have plagued them the whole time. Both of their pasts are star-studded, as well. Jessica was famously married to Nick Lachey, and she dated John Mayer before moving onto Romo. For his part, Tony has romanced Sophia Bush and Carrie Underwood (though Jessica insists there's no feud between Carrie and herself. It's sad but true: There's little reason to believe this couple will last through 2009.

Nicole Kidman & Keith Urban

Both of these celebs have a rich dating history in the most literal sense. Nicole was famously married to Tom Cruise for 11 years, with whom she adopted two children. Keith dated a non-celebrity for eight years before moving onto model Niki Taylor in 2002. Still, they've been married for a couple of years now and have a baby girl named Sunday Rose.

Jennifer Lopez & Marc Anthony

Rumors awhile back claimed that Jennifer Lopez & Marc Anthony were on the rocks (she allegedly resented that her movies were way more successful before he stepped in), and it didn't help when she was seen out without her wedding ring. But Lopez gave birth to twins Emme and Max in 2008, and the couple seems just as solid as they've been for their five years of marriage. Even though J. Lo has some high-profile relationships in her past (think Sean 'Diddy' Combs and Ben Affleck), these two seem content with the family they've built together. And to appear in dramatic music videos together:

Vanessa Hudgens & Zac Efron

The couple's youth works against them on this count. It's safe to assume that they'll move onto more projects, meet more sexy costars and fall head over heels again. Besides, Zac has said publicly that he's not interested in settling down anytime soon.