I'll start with listing where I have ordered from:
Twojliquid.pl
baseliquids, nic (highest is 36mg/ml), FA tobaccos, other flavourings (including malic acid, menthol crystals, Tobacco Absolute), bottles & pipettes. No
vaping gear, no pre-mixed liquids.
The site is only in Polish, but with Google translate it is quite understandable. They answer emails (in English) quickly. Shipping is a bit expensive (~15 euros), but nothing else is.
Liberty-flights.co.uk
Carries almost everything (unflavoured nic @ 25 and 50mg/ml - haven't tried it). Free shipping. I have bought cartomizers, atomizers, a few flavours and liquids.
Not cheap (especially not compared to twojliquid), but very established and a good selection.
Ecigoutlet.co.uk
I bought Hangsen-concentrates (very good selection). Very fast shipment, not expensive (non-trackable). They also carry gear, Hangsen DIY-kits and unflavoured liquids (in very small bottles).
Two more I know of, but haven't ordered from yet are:
flavourartexpress.biz
(not only flavourings, they also have some nic-liquid, up to 36mg/ml)
inaweraflavours.com
(Also Polish, their tobaccos and bases (several different varieties, up to 38mg/ml in strength) get good
reviews.)
I am now getting to a point where I am no longer "playing around to see if I like this whole thing", so I am starting to get really envious of our US-based fellow vapers with their huge variety of nic-vendors having sales all the time!
For economical reasons I am starting to think about maybe getting my nic in a higher strength, but so far the highest I've seen has been L-F's 52mg/ml.
Or getting bigger bottles - my ~80ml 36mg/ml from twojliquid will soon be used up if I continue mixing experiments* at this rate. L-F offers 250ml bottles, Inawera up to 5 litres (1 litre might be a more suitable size).
Anyone seen 60 mg/ml or even 100 mg/ml for sale within the EU/EEA?
What about really good deals?
Both on nic-liquid and on PG or VG in bigger quantities?
(Any fellow Finns reading this: have you found PG or VG locally at a tolerable price? Pharmacies sell aquous glycerine in smallish bottles, but no pure glycerine. PG I have so far only seen as an ingredient in a cattle product - I wonder if betaine is good to vape? 
It irks me to pay lots of money for things that should be really cheap if bought in bulk (or pay oodles for shipping of a cheap product) - and as I'm playing around with extracting my own flavours from tobacco, coffee, spices etc I could well use a few litres each of PG and VG.)
*Yes, I have heard of the idea to mix zero-nic and only add the nic when the taste is good - it doesn't work for me. For me, who mostly only mix tobaccos, the nic is an integral part of the taste and zero nic just doesn't tell me anything about the real taste of a blend. I economize a bit by often mixing lower nic for trying out a taste, but no nic just changes the flavour too much for me.