Grats!! I love my Riva 510 too! Somehow the 3.7v Riva 510's from LF seem to have a bit more punch than my 3.7v mods.
Be careful not to over-screw anything in or on including the charger. Things should only be screwed on just far enough to connect and work. And always clean the threaded end with soft tissue before putting it on the charger. Also, if you own any slim 510 batteries never charge them on the Riva's fast charger. Slim 510's need their weaker charging cables that only put out 150-250mA of power. The Riva charging cables usually put out about 420mA.
The most popular thing to use on Riva 510 are probably Boge 2 ohm cartomizers (most popular cartos on all 450mah+ 510-threaded devices).