If you're heading downtown to check out those many Lincoln sites or the Illinois capital stuff, there are a few places with vegan options. I like to go to Cafe Brio where they give you chips and salsa to start and I always get their spring salad. For sandwiches, one is kinda at a loss for a vegan grub, but they have a portobello sandwich which you can have them veganize (no pesto and aioli). This pretty much just leaves you with bread and a mushroom, so get some sandwich veggies and mustard and you're good to go. They have some pretty tasty hand-cut fries and sweet potato chips too.
For a complete review, please see my blog here: http://veganmiss.blogspot.com/2011/08/vegan-springfield-il-part-one.html
Cons: needs more veg options on menu