I think most Protestants believe that you can be from a different denomination and still go to heaven, although they usually think their denomination’s beliefs and interpretations of scripture are the most correct. Personally, I am bothered by the proliferation of Christian denominations and think it hurts the heart of Jesus because I don’t think He meant or wanted Christianity to be divided like it is.
With that said, I think certain denominations have certain strengths that, if combined with those of others, would really be awesome for the cause of Christ. For example, I remember the sense of reverence I felt as a child in the sanctuary of the Presbyterian church of my parents. I think Baptists in general do a great job of teaching children how to memorize scripture and learn Bible stories – some of these kids are like human Bible encyclopedias. I think Pentecostal and non-denominational congregations are very welcoming and stress the work of the Holy Spirit in a charismatic sense. Many Methodist, Lutheran, and Episcopal churches combine liturgy with an evangelical zeal that is quite commendable. Catholicism, of course, has all the sacraments and can legitimately argue that they were the original Christians that can trace their spiritual lineage directly back to Christ and the disciples.
However, I think certain theological differences are divisive – some major and some minor. For example, some believe communion is really the body of Christ, most others believe it to be symbolic. Some believe in infant baptism while others believe a person should have a spiritual awakening and profess faith in Christ before being baptized. Of course, the abortion issue is a major divisive issue within Protestant groups – the more conservative ones lean pro-Life whereas the more liberal lean Pro-Choice. The list goes on and on.
In summary, I think the answer depends on who you talk to. In my view, the existence of so many denominations confuses non-Christians and may cause them to hesitate before considering Christianity as a faith option due to the lack of unity.