Ultra long ETFs
Ultra long ETFs (2 times return of the underline security):
Ultra QQQQ: QLD
Ultra Dow: DDM
Ultra S&P500: SSO
Ultra MidCap: MVV
Ultra SmallCap: SAA
Ultra Russell600: UWM

Short ETFs
SDD. Ultra short S&P 600 small cap.
TWM. Ultra short Russell 2000.
SKK. Ultra short Russell 2000 growth.
SKF. Ultra short Financials.

International and sector ETFs
FXI. China Large cap 25 companies.
PGJ. Power Shares China ETF. Contains all of FXI's holdings, plus lot of small companies.
EWA. Australia ETF. A good indirect play with currency and commodity as well, since Australia has lot of mining companies, and its currency may strengthen against dollar.
EWC. Canada ETF. Has many energy companies and mining companies.
EWT. Taiwan ETF. Has high tech companies.
EWJ. Japan ETF.
EPP. iShares MSCI Pacific ex-Japan. Has companies from Australia, Hong Kong, New Zealand, and Singapore.
EEM. Emerging market.
EWZ Brazil.
EWW. Mexico.
EWY. South Korea.
EWQ. France.
EWG. Germany.
EWH. Hong Kong.
EZA. South Africa.
EWD. Sweden.
EWU. UK.
JSC. Japan Small Cap.

Sectors:OIH. Oil drilling and services companies.
XLE. Energy companies.
GDX. Gold and silver mining companies.
GLD. Gold.
SLV. Silver.
USO. Oil.
PHO. Water ETF, a long term play.
IBB. Bio-tech.
IYH. Health care.

Currency ETFs
UDN. Short US Dollar
UUP. Long US Dollar
FXE. Euro. This is the first one and with about 1B asset, the largest currency ETF. Yield is 3.28%.
FXY. Japan's Yen. Yield is 0%. That is, return is negative if Yen is flat against Dollar since you pay the 0.4% fees.
FXC. The Canada's dollar. Yield is 3.78%.
FXA. Australia's dollar. Yield is 5.73%.
FXB. British Pound. Yield is 4.95%.
FXM. Mexican Peso. Yield is 6.28%.
FXF. Swiss Franc. Yield is 1.25%.