Really depends on the budget you have available. I would think that something like the Ecosse Composer (at £29) interconnect and Ecosse CS2.2 (£2.60 per metre) for speaker cable will allow your system to reach it's potential without opening it up too much to reveal the inherent flaws. Both are well regarded and relatively inexpensive.
If you actually fall into the 'cables do make a difference' camp, you may as well also accept the logic that it makes sense to 'match' cables throughout the system and use cables from the same manufacturer as they're obviously going to R&D their products using their own cables.
Army Bloke is correct though, basically buy the best you can afford up to around a maximum of £50 interconnect and £6 per metre speaker cable for the system you have. Anything more expensive may well give you a worse return on your investment.
If I were you, I'd try to borrow some from a dealer before you go spending a large amount of money on these items.
See if you can actually hear any difference (let alone improvement) first.
If possible try to do any listening tests blind (ie so you don't know which cables you are listening to) - you may be quite surprised by the results.
The subject of cables is arguably the hottest potato in hifi at the moment. I think most of it is hugely overhyped, especially when using budget (but still decent) kit.
Many of the people who can (or think they can) hear clear differences between cables when they know what they are listening to, struggle to hear any difference at all when they are "blind". (I used to one of the former, but am now happily in the latter category, as are several other people I know who've bothered to actually investigate this issue themselves, and not just rely on magazine reviews. I've yet to meet anyone who has done any research like this, who still thinks cables make any real differences (although a cable "maker" will no doubt argue this to death) - and certainly nothing to warrant the ridiculous prices they are charging for some of this stuff).
Interestingly, I know of no cable "manufacturer" who has ever agreed to take part in any study of this kind, despite several invitations (mostly in the USA).
You can do a web serach for some of the articles!
But you don't have to believe me, just try it yourself - once the mind tricks have been removed from the equation, there's little substance left in the argument IMO. If you can still hear that one cable definitely sounds better than another, then buy that one - you've really lost nothing to try it first!
With very high end equipment, there "may" be a little more substance to the argument, but then huge compromises haven't been made elsewhere in the system, which are several orders of magnitude more audible than any cable differences.
Spend your money on some CDs to actually enjoy on the system instead of this "smoke and mirrors".
It's hard to recommend anything specific, as I have no idea what products you have access to in Slovenia, or what the general price levels are like there - what may seem cheap in the UK, may seem very expensive to you, relatively speaking, and vice-versa.
In the UK, some hifi dealers are making up to 1000% markup on these products - basically they are ripping you off, but there seems to be no shortage of eager punters willing to pay it (maybe I'm in the wrong business).
As a guide, I'd be looking to pay no more than £20 total to connect your kit up with both a 1m interconnect and say 3-4m of speaker cable to each speaker.
cables tend to make subtle differences to a system, they are not a panacea for a poor system.
Its a bit like adding an extra bit of seasoning to your soup.
Although there are definite differences in the sound of each cable, you can only really decide after extensive listening in your own home, not at a dealers.
My advice get some decent cable to start with, not bell wire etc, but do not pay loads 2.00 or 3.00 UK pounds per metre maximum.
If you feel that you would like to try different combinations once you are happy with the initial set up, then borrow cables from a dealer for a couple of nights.