This is my domain! I've camped on ice sheets at -30c and hammock camped in monsoons.
Some good suggestions so far, but people have a tendency to just suggest what they have rather than what is actually best for you or your application. Seeing as I probably have more camping kit that most shops, I'm happy to give impartial advice!
First question needs to be where are you setting up camp? Are you on a hillside or woodland, how far from your base (car / house) will you be walking and for how long? What pack will you be using?
Bivvi bags are great, but you get what you pay for and if you're out for multi-day trips you'll want respite from mozzies. A decent breathable bivi and tarp will actually take up as much room in your pack as a good one man tent, but the tent will give you a comfortable place to relax away from pets, get changed and keep your file away from the elements.
MSR or Terra Nova would most certainly be my go-to brands to recommend for a light weight backpacking tent. Quality from both are excellent and you'll get something that is durable and tested to extremes. Don't be fooled by cheap Chineese knockoffs on Amazon. Please. Not if you want something that will last more than a few outings.
For complete space saving and light weight you may want to look at the MSR Hubba NX Solo:
A leader in outdoor equipment innovation, MSR is dedicated to engineering high-quality stoves, tents, water filters, snowshoes and more to help people worldwide unlock their greatest adventures.
www.msrgear.com
This actually packs smaller than my ground sheet, gore-tex bivi and tarp, but can also be used as a hooped bivi if you want to go ultra light in the summer without the inner tent. The down side is space. It offers a nice place to be, you can sit up fully, but your pack is down by your feet or in the small porch if it's dry.
If you don't feel you can justify that price then the Wild Country (Terra Nova's less expensive brand) Zephyros 1 or 2 are fantastic value. You don't get as much headroom, but you get a little more width but you pay for it with a little extra weight. I think I have 6 mates with the Zephyros and it probably offers the best bang for buck. It's not as easy to pitch and doesn't offer the outer / footprint only combo that the MSR offers, but seeing as the Hubba is so light I rarely bother not taking the inner tent for the comfort it offers.
Looking for a lightweight tent that takes the minimum of space in your rucksack? This packs down to just 30x18cm and weighs only 1.57kg. An ideal for backpacking and travelling companion.
www.terra-nova.co.uk
If you're camping in or around woodland then I'm a big hammock fan. I've never slept as well outdoors as I have done in a hammock. The last time I was out I slept for 10 hours! The downside to a hammock is that for a decent setup you're looking at a fair cost and they're not as compact as a quality small tent.
A hammock offers the advantage of being off the ground. It also offers the disadvantage of being off the ground. You have no insulation under you and a sleeping bag alone is not enough. You either need to use a softly inflated mat under you, which will inevitably end up on top of you in the middle of the night, or you need to invest in an under quilt. A decent down under quilt will set you back as much as a decent down sleeping bag. Or you can make one quite easily if you're brave with a sewing machine (YouTube tutorials are aplenty).
As far as hammocks go there's a decent amount of choice these days. For anywhere in Europe you need one with an integrated mozzie net. I cannot stress the importance of this enough. If you're happy to tinker and modify to your specific needs then Hennessy are an excellent option. You will probably want to modify the suspension system, but they are a great system.
The Hennessy Hammock is the most innovative solution to lightweight, comfortable camping. Learn more about our designs and features, and buy directly from the manufacturer.
hennessyhammock.co.uk
If you want something that is great out of the box then the Thermarest Slacker Hammock House is brilliant. No need for modification or upgraded suspension, but it's not as 'stealth' or as light as the Hennessy.
The all-in-one hammock shelter, ready for camping adventures.
www.thermarest.com
Both systems will need an under quilt. Don't bother messing about with any other type of insulation, I've tried them all and an under quilt is the only way to go with a hammock. Again, don't be fooled by cheap knockoffs, they just don't last. A mate bought one on Amazon and he ended up on the floor the first time he used it.
I guess without answers to the questions at the start of this in summary I'd suggest:
- Need for ultra light, one night and on loamy or mossy ground - Quality Gore-Tex (or similar breathable fabric) bivi
- Multi day hillside or you want a little more comfort and shelter from elements / midges - Light weight quality 1 man tent
- Woodland multi day - Hammock with tarp, net and underquilt