I have a Sigma 28-70/2.8, I haven't used it much but will now be using it again a lot. However, I took it out of the Ziploc baggie I had it in, and it seems to have some fogging on the inside of the front element. I'll look at it better tonight, but it didn't look like fungus. Heck, it was put in the baggie just a few weeks ago, but before that it was stored with those silica gel packs. The trunk in which it's stored also has gel packs in it. And the Ziploc should be airtight...

Is this something that can be cleaned? Would it be worth it? It's the higher-end 28-70, but still well under $300. Maybe it's time to sell a few things and pick up a real-deal Canon L wide-angle...

You could try exposing it to sunlight for a while, but don't let get so hot that the lubricants run and make things worse.

You might give Sigma a call. Perhaps the have a quick/easy fix.
http://www.sigmaphoto.com/contact/contact.asp

Thanks, guys. I'm sending it off to Sigma, they'll give me a free estimate, so I can decide from there.

if there is a repair shop in your town they can pop off the front element and clean it... but I would not be surprised if there wasnt more fungi in the areas you cant see

Yeah but the shops in my area send it out to the manufacturer, for the most part - and they charge an average premium of $25 to do it.

If it doesn't work out, then I'll just sell it for cheap on eBay along with a cheapie Sigma I have in the same range, and put the cash towards an L lens.

I was out in Moab Utah one time shooting a model.  I had a canon 50mm 1.4 that just would not focus right.  There was something wrong with the connection between the lens and camera body.  Auto focus.  It just would not pick a spot to focus on.  So after about 3 days of that I threw it off a 1000 foot cliff.  In about a 1000 years somebody is gonna find that out in the middle of nowhere and wonder " HOW THE HELL DID THIS GET HERE".  BS