Most extensions written for nBill will work with nBill Lite. This includes payment gateways and language packs. Some feature extensions will not work with nBill Lite - nTicket, nCart, and the cPanel automation extensions rely on the order form feature of nBill, which is not present in nBill Lite, so they will not work on the Lite edition. The enhanced domain name checker is also not applicable to nBill Lite as it is only useful on order forms (technically it could be used on client profiles in nBill Lite, but there is not much point in that).
Please refer to the main nBill website for nBill extension downloads.