I lease my 159, and its a good option for Alfa's since the depreciation becomes the finance companies problem after however long. 2 Year deals are good, since you don't get bored of the car, and you might even get away with not replacing tyres in that time. Sometimes 2 years lease are on offer, otherwise you usually pay through the nose.
Things to watch for:
Fees at the end of the lease, for what the leasing company terms as beyond "normal wear and tear", so things like parking dings, kerbed alloys etc can be "charged" for (although I got out of it twice by just being really awkward to Lex leasing).
I got my 159 from Mangoletsi, who actually are brokers for Fiat Finance. here is the link to the Brera deals.. Mangoletsi, Alfa Romeo and Fiat Dealership in the north west of England - Alfa Brera
My contact was Kevan who would probably tell you what the next Alfa incentive will be (I think it was going to be GT's next from memory)
Car leasing - Contract hire and car leasing special offers
is always a good way to check loads of brokers, although it usually ends up that they all offer whatever incentive the manufacturers are doing at the time. The only time you deal with the broker is when you sign the deal (and usually give them some money for the privelidge), then its the finance company/dealers after that.
Advice would be get a car which is standard with the spec you want, rather than adding options on, as you basically pay for any extra's in full over the term of lease. Cars like LE's and Ti's are good since you don't have to add anything on.
Before 159 I had a 3 series on a 2 year deal, and before that an A4 on 18 months. Short term leases are good, but you end up paying the 3 payments up front more regularly