You can polish them out with decent success if not too far gone. Otherwise places like RockAuto or eBay for replacement pairs. Many people go aftermarket with projector headlights but I have heard of people complaining about light output not being great.
If you have an 03-05 you can upgrade to the 06-09 projector headlights, below is a great thread discussing what needs to be done to swap.
i have the TYC projectors on my 04 and no complaints...think i paid around $90 each for them on rockauto. worth checking amazon too for the tyc or depo
just get oem brand new from toyotapartsexpress.com
was the cheapest place to get a pair for under 450 out the door, i think they do sales on tuesday and fridays, i get some email about 15% off sometimes.
Occasionally a used OEM set pops up for sale on the for-sale threads around $100 for both. That's how I snagged my 06-09 upgrades, Polished them up, almost looks new from up close.