Here's my latest budget boner
The Mach Audio MLI-65
http://www.mach5audio.com/index-2.html
Coupled with this tweeter
http://www.pacparts.com/part.cfm?CFID=767269&CFTOKEN=85991391
Under $100.00 after shipping for some very nice speakers.
Run them active and you have a pretty nice setup that you can brag only cost you "X" amount of dollars.
The mid that DejaWiz recommends is rock solid as well, albeit a bit difficult to work with. If a large format tweeter isn't your cup of tea, then the Seas Neo is a great option, and will match up decently with the RS180.
http://www.madisound.com/catalog/product_info.php?manufacturers_id=149&products_id=628
If you feel you may get the upgrade bug down the road, the Seas Neo is a great place to start as it's a very versatile tweeter, and performs up there with tweeters much, much more expensive.
The Alpine tweeter is a derivative of Vifa's XT19 which is a highly regarded home tweeter. Beautiful sounding tweeter, but special attention needs to be paid when picking mids to match up with it.