to add, here is the english to sindarin version of one of the sites above
http://www.jrrvf.com/hisweloke/sindar/online/sindar/dict-en-sd.html

If you'd like to study Quenya I recommend starting with Helge Fauskanger's course on Ardalambion:

http://folk.uib.no/hnohf/qcourse.htm

First step though would be to read what Tolkien wrote about the languages and the Tengwar in the Appendix of LoTR.

Here are a few links I've come across:

http://www.thetolkienwiki.org/wiki.cgi?FrontPage

http://www.quettar-orenyallo.ch/ -> A collection of Neo-Quenya with translations

http://www.jrrvf.com/~glaemscrafu/texts/index-a.htm
-> Check out the "Read by Tolkien" section

http://elendili.pl/viewforum.php?f=22

http://www.forodrim.org/index_en.html

http://www.realelvish.net/

Good additions, thanks!

Some other additions, off the top of my head:

http://www.sindanoorie.net/
http://www.ellammath.de/
http://www.oocities.org/elenyona/ (as Geocities is no more)

I'd have to load my older set of bookmarks to see what other sites I recall are still around, and what aren't.

In addition to www.realelvish.net another really good source that I've been using for Sindarin is http://sindarinlessons.weebly.com/