Almost all veg is fine other than potatoes and beans (green beans are fine). My like tomatoes, corn, cucumber, carrots, lettuce, kale, beets, carrot tops, wild plants, basil, sage, lemon balm, etc. They're not huge fans of fruit but their favorite treat is dried carrots. They go CRAZY over them!
Hello and welcome to the forum.
In the top bar there is a section called Guinea Pig Guides, if you look in there you will find the Diet Guide. In the diet guide there is lots of useful information as to suitable food and how much to feed. There are lots of really useful guides in this section, they are really worth reading. Guinea Pig Care & Information Guides
Mine like all sorts of veg from lettuce (not iceberg though don't give iceberg to piggies)to aubergines (egg plant) and all things in between! I gave mine their veggies tonight before I had had a chance to peel the carrots and they all looked at me as if to say "Oi where's the carrot?! what sort of slave are you hoomin" I won't be doing that again!