I just use a regular 10/40 semi synth - not anything mega expensive - Castrol, Duckhams etc - but a known brand. genuine oil filters are available from David Silver for less than a fiver, I often use Hiflow filters from Ebay (HF112) that can be bought for £2-3 if you shop around and they have been OK.
THE IMPORTANT THING is that you need to change the oil every 1000-1500 miles and the filter every second or third oil change - ignore what it says in the manual (5000 miles) or you may end up with top end problems.
Checking the oil level on the dry sump engine can be tricky - a recent discussion here amongst owners concluded the most reliable way is to take the bike for a short run from cold - 2 or 3 miles - then as soon as you stop let it tick over for 3 minutes then dip the oil tank. Again the method given in the manual is not a very good indicator.
