Since we have NO previous knowledge of your tables and how they're used, we need specifics to make any reasonable judgements. It's rather frustrating when we ask such things to be told, "our current code, table design and hardware are perfect, it's just running too slow." Hmm, doesn't it seem that something must not be perfect if your response time is that slow?!
At a minimum, I don't feel comfortable without looking at missing index stats and index usage stats. I can provide a query for you to run that will give us those stats. I, and others here, can then agree that indexes are great as is or suggest changes. However, if you're not going to make any changes anyway, you're right to tell us that now, and please do so. I don't want to waste time designing changes you won't consider anyway.
Also, after I see those stats, if I believe your existing indexes are not perfect -- in particular, if the clustered index(es) seem wrong to me -- then I can comfortably drop out once I know you're not going to make changes to them. Because, as I see it, with the wrong clus key, you will forever have performance issues and relegated to constantly tweaking non-clustered indexes. And personally, I have no interest in volunteering for that, it's just not for me.
SQL DBA,SQL Server MVP(07, 08, 09) A socialist is someone who give you the shirt off *someone else's* back.