The CaribbeanThere are lots of deals right now. I just went to Turks and Caicos using Lastminute.com, but there are other options. With Lastminute, you often have to check carefully for catches, like overnight flights, or trips priced for 2 if you're not going with someone. (I like solo travel, because I get to read more.) CheapCaribbean is one site that I think a friend and I used for an all-inclusive Cancun trip a few years ago. It's not hard to find resources like this. I've enjoyed winter trips to St. Croix and Grand Cayman for snorkeling using these types of sites. You'll still want to find a good site on the destination itself, to help you pick your hotel location, if you're not driven solely by price.
Adventure TravelA few years ago, a friend recommended this site Adventurecenter.com and their trips (she'd been on 2). I've been a drooling over their catalogs for the past several years myself, ever since going on a very wonderful trip to Morocco that they advertised. They offer group travel for active adults, sporty or cultural or no-frills, sometimes with an eco-orientation. I wouldn't go to Morocco alone, and I'm not sure I'd even go with just a female friend. But I had a terrific time in a group of young adult (mostly UK-based) adventurous travelers. It may have helped that an Irish woman brought along a bottle of gin. Note that their prices do not include the airfare, while the Caribbean deals above generally do.
Another adventurous option, solely in the UK, are the National Trust volunteer working holidays. These are also group trips, based in one spot, usually with lodging in a youth hostel; you are doing some type of local volunteer labor while there, with breaks for genuine sight seeing and socializing built in. The ages are quite mixed, without any young kids along. I myself did an archaeological survey trip in the Midlands. Lots of fun, albeit also some hard labor clearing off brush from a buried hill fortification. (I see their web site now says that for legal reasons they are currently only accepting EU and Swiss residents for their bookings. How sad!
A friend recommends EarthWatch expedition volunteer trips, but I find them a bit expensive for my tastes. There are some volunteer trips in the AdventureCenter catalog, as well. I'd like to know about more that are not extremely pricey, if you want to leave a comment or send me email?
Rentals in FranceI know this is a bit specific, but since I did it recently (and have done it on and off for years), I thought I'd post the how-to's.
The primary source for good-value housing rentals in France (not Paris, but the rest of the country) is the French Gite system, on the Gites de France site (English available). Originally all arranged by paper catalog, it is now online, and many of them take internet bookings directly via the site. Normal reservations during high season are for weekend to weekend only; outside of high season, you can negotiate for different days or less than a week.
A few things to be aware of: You may need to pay a deposit or full amount in advance (by wire, or they may agree to hold a paper check); you often have to pay a surcharge for water, heating, and other fuel costs, and often for bed linen and towels. You are expected to clean before you go (they are not hotels - think of it more like a well-equipped private hostel). But if you can handle this, there are many beautiful farmhouses, cottages, and apartments, often old historic ones, for a steal - especially if you split the cost.
I admit I went out of the system for my recent Brittany vacation because it was easier to search for wifi on this UK site, French Connections. (Yes, it sounds like a bad dating site.) Some of these rentals are also cross-listed in the Gites listings.
Rental cars are easy to hire in France, from Avis, Alamo, etc.; use their sites, or a local European wholesaler like Nova. Pickup options that are most convenient are train stations in the main towns (I used Rennes) or airports. Even tiny airports that are taking RyanAir and other discount airlines have rental car options. It's much cheaper to get a manual transmission, but you can reserve automatics too.
The French train system requires reservations on many lines, and the TGV especially: You can use this RailEurope site instead of the SNCF site to book an electronic TGV ticket with a claim code that allows you to retrieve it at a kiosk at the station in France.
Paris rentals are a lot pricier. There are a zillion sites out there - use at your own risk, or get a hotel.
FYI, my trip recently was Boston-London, cross London by bus to Stansted airport, fly by cheapo Ryan Air (bought on their site) to Brittany (Dinan), pick up car there, drive to apartment with wifi. This was because I got a much better deal on a ticket to London at the time, and it saved me 2 train rides and a lot of time to go via Ryan Air direct to Brittany rather than travel via Paris.