I know that the stocks/ETFs UNG and GAZ are tied into the price of natural gas but supposing I have a stock trading account but no commodities like forex, gold, oil etc. Is there a way I can bet on the price of gold and the price of oil through a stock rather than having to open a forex account?

Answer
Yes,

1x long gold
SPDR Gold Shares (GLD)
http://finance.yahoo.com/q?s=gld

2x long gold
PowerShares DB Gold Double Long ETN (DGP)
http://finance.yahoo.com/q?s=dgp

1x long silver
iShares Silver Trust (SLV)
http://finance.yahoo.com/q?s=SLV&=

1x long USD
PowerShares DB US Dollar Index Bullish (UUP)
http://finance.yahoo.com/q?s=uup&=

oil/ and related
iPath S&P GSCI Crude Oil Ttl Ret Idx ETN (OIL)
http://finance.yahoo.com/q?s=oil&=

Energy Select Sector SPDR (XLE)
http://finance.yahoo.com/q?s=xle&=

2x long
Ultra Oil & Gas ProShares (DIG)
http://finance.yahoo.com/q?s=dig&=

2x short
UltraShort Oil & Gas ProShares (DUG)
http://finance.yahoo.com/q?s=dug&=

Oil Services HOLDRs (OIH)
http://finance.yahoo.com/q?s=oih&=

to name a few...

Which stocks or ETFs are linked to the price of gold?

I know that the stocks/ETFs UNG and GAZ are tied into the price of natural gas but supposing I have a stock trading account but no commodities like forex, gold, oil etc. Is there a way I can bet on the price of gold and the price of oil through a stock rather than having to open a forex account?

Answer
Yes there is, you do not have to open a forex account - the ETF that track the price of gold is 'GETF'. Search for it on Yahoo's ETF section in the finance page.