A great Temecula venue that's a favorite is the Temecula Creek Inn. http://www.temeculacreekinn.com/weddings.html. It has this amazing Stone House and outdoor ceremony and reception site that is far removed from the golf course and hotel. It's a super grassy, rustic, and spacious location and I love it! What I love even more is that they golf cart the guests to and from the wedding site and their hotel rooms (which means all eat, drink, and be merrying you can handle).
I also love the Faulkner Winery in Temecula. It has a large restaurant with a 180+ degree view of Temecula Valley complete with two outdoor ceremony sites, an outdoor deck, and it's super private. http://www.falknerwinery.com/weddings/weddings.php Notice a trend... :) I love a more personal, intimate setting.
Other wineries to consider are South Coast which is a huge spa, hotel, and winery and a lot of fun! Ponte, which has a great Barrel Room that you can have your reception in (but be sure to bring a sweater or a wrap). And of course Wilson Creek has a great Almond Champagne! They also redid their whole venue to better accommodate larger weddings and events.
If you know of other venues I should have mentioned or check out let me know!