Lauren Conrad might be old as the "Hills" ... but she's still rich as ever ... plunking down $3.74 million on her new L.A. mansion.

Sources close to the deal tell TMZ, the 27-year-old former MTV star purchased the 4,300 sq. ft. 6-bedroom, 5-bathroom Brentwood home this week.

It's two stories ... with a brand, spanking new kitchen, huge backyard and a basketball court. It was remodeled recently by celeb interior designer Jeff Lewis from Bravo's "Flipping Out."

Not a bad purchase ... especially for someone who used to be best friends with Heidi Montag.

While most of the country is freezing their asses off, former "The Hills" star Audrina Patridge warmed her sexy bones by slipping into a tiny bikini and hitting the sand with her pup in Manhattan Beach.

The 27-year-old is the perfect cure for the winter blues. 

Former "Hills" star Audrina Patridge is selling her bikini-clad body (again) -- stripping down for a smoking hot 2013 swimsuit calendar -- and TMZ has every month's picture.

Trust us, it's awesome. In fact, it has everything you could ever hope for ...

Audrina's boobs ... check.
Audrina's boobs oiled up ... check.
Audrina's boobs by a pool ... check.
Audrina's boobs on a chair ... check.
Audrina squeezing a dog in her boobs ... check.

Seriously, check.

Former reality trainwreck Heidi Montag took a break from living in obscurity to wash up on the beach with all her augmented fake body parts in a skimpy red bikini in Santa Monica on Wednesday.

The 26-year-old former "The Hills" star -- who infamously had 10 plastic surgery procedures in one single day back in 2009 -- did some of her best acting while hamming it up for the cameras on the sand.

Who needs a lifeguard when you have built-in triple D floatation devices at all times?

Former "Hills" star Audrina Patridge celebrated her 27th birthday at Wet Republic at the MGM Grand yesterday ... by donning her customary two piece outfit.

Like some parts of Audrina, seeing her in a bikini never gets old.

Former "The Hills" actress Audrina Patridge took time off from her busy schedule of wearing a bikini in L.A. ... to show off her slammin' body in a white hot bikini at the ME Cabo Hotel in Mexico yesterday.

Audrina is down in Cabo San Lucas celebrating her 27th birthday with her BMX boyfriend Corey Bohan and some family members.

All of Audrina has grown up quite nicely.

Former MTV star Lauren Conrad is back on "The Hills" -- Beverly Hills -- because she just dropped $1.35 million on a swanky new condo in the wealthy L.A. neighborhood.

The ex-reality star will be the newest resident of the 90210 -- recently purchasing the massive 3,200 sq. ft. 2-story, penthouse condo with 3 bedrooms, 4 baths, and a 24-hr security system ... to keep away all those crazy "Hills" fans.

The house also sports a rooftop pool, outdoor deck, full gym, indoor bar, marble bath and hardwood floors.

But all this doesn't come cheap -- Conrad has to shell out $2,319 in homeowners' fees alone ... and then pay her million dollar mortgage on top of that. Oh, and this is her 2nd house -- the other one is in Malibu.

All hail LC.

Kristin Cavallari has some problems back on the home front ... because her family has officially lost their ocean-front mansion featured on "Laguna Beach" after falling behind on mortgage payments.

The house is INSANE -- 5 bedrooms, 5 baths, ridiculous infinity pool, dry sauna, wine cellar, yoga room and some of the sickest beach views you've ever seen in your life.

But TMZ has learned ... the bank recently foreclosed on the property because, according to official documents, KC's father Dennis failed to make payments on the $7,599,458.66 he owed on the place.

And now it's too late for the Cavallari's to get the place back ... because the house was sold at a public auction just last month for $6.1 mil.

Calls to Kristin's rep have not been returned.

It seems reality stars are getting knocked up left and right these days ... Snooki, Jessica Simpson, Kristin Cavallari, etc. ... but not Audrina Patridge ... at least judging from the way she looks in her bikini.

Congratulations.

Former "Hills" villain and half of one-time reality TV D-list supercouple Speidi ('memba them?), Spencer Pratt proved he's even larger now (left) than in his 2009 heyday (right) as he left a gas station in L.A. on Tuesday.

Look out K-Fed, because this is how Spencer rolls.

For a second it seemed to be 2009 all over again, as once famous famewhores Heidi Montag and Spencer Pratt (Speidi, anyone?) pretended to not know they were being photographed as they did something -- in this case, act all lovey dovey while skiing down a mountain -- on Thursday.

Seeing "The Hills" dynamic duo again makes one feel really thankful for the "Jersey Shore."