Both old lei banknotes (10.000 to 1.000.000 lei polymer) and new lei (four zeroes cut) are now in circulation here in Romania. As I know at National Bank are for sale (or it was until october 2005 - my last visit at National Bank) only uncut sheets of four banknotes in old lei. I do not collect banknotes. About coins, I know that the mint set 2005 presents old and new lei coins, but it was about a 1000 sets. Commem coins are at more ridiculous mintage, between 150 to 500 pieces... Almost nobody here collect them because it is virtually impossible to complete a set of commems, and more important, it seems that into black market exists a flood of commems without certificate from National Bank - it seems like an "unofficial" mintage, because of perfect quality. So, my advice is to not buy commems 1996-present. The same thing about patterns: it looks like for some coins exists more patterns than the official mintage of "regular" commems. I say "pattern" because they are made from different metal, but also in proof and in mint quality. Something stinks at Romanian Mint...
About regular circulating coins (new 1 ban, 5 bani 10 and 50 bani), if somebody is interested I have some opened rolls.
About banknotes, the smallest: 1 leu is worth approx 40 cents, and the biggest:500 lei - approx 200$. Right now exists 1, 5, 10, 50, 100 and 500 lei, and next month will be issued and the 200 lei banknote. The dimensions are the same like euro banknotes, but lei are in polymer, and of course different design.
For more infos:
http://www.denominare.ro/common/htmls/en.htm