We call them all, colloquially, accountants. But some folks who do taxes are CPAs, some are tax attorneys, and some are neither. If your business and your return are on the complex side, you'll want a CPA or a tax attorney. If you get audited, you'll probably need the attorney.
There's more art than science to taxes, and much depends on how aggressive or conservative your accountant chooses to be. If you are cautious by nature, get a cautious accountant.
The IRS tracks returns by industry, so make sure your accountant is familiar with the standards in yours. And if you have a complicated tax situation--investment real estate, say, or overseas transactions--make sure your tax preparer is versed in the arcana.
You need to know what your accountant's role will be if there's a problem. How much experience does he or she have with audits? Most CPAs and tax attorneys will handle the case themselves; part-time accountants likely won't--and aren't qualified to do so. Enrolled agents--who are often former IRS examiners--can also represent you in an audit. Whomever you hire, you'll want that person on your side the moment you get the first notice from the IRS.