I'd like to recommend NFD, but I'm the lead dev for it so I'm biased.
NFD is a plain clone of Nxt, so it has all the functionality of Nxt at a much, much cheaper price. Admittedly, it's really cheap because NFD's ecosystem is bare-bones at the moment. But we're working on bettering it.
So, NFD is a pure speculation at the moment...but if you want to play around with a Nxt-compatible clone, you can get in very cheaply.You can buy all you want at 3 satoshis.
http://www.nfdcoin.com/Unfortunately, the only major exchange that trades NFD atm is Bter...and they've suffered a huge loss from a hacker stealing ~50 million Nxt. No NFD was stolen, but more than a million dollars' worth of Nxt were.
http://cointelegraph.com/news/112278/breaking-bter-hacked-50m-nxt-stolenYou may still be able to trade NFD at Bter, but a small withdrawal I made at ~ 7 AM Eastern time is still "Processing" - i.e., in lockdown. With this warning in mind, here's where you can pick up some NFD if you want to speculate on it or try it out:
https://bter.com/trade/nfd_btcThe last-trades list indicates that trading is active. If you decide to go in and you're lucky, you might pick up some at 2 satoshis.
The official NFD thread is here:
https://bitcointalk.org/index.php?topic=603932.2160;topicseen