You do not need to use the .com in your LLC name. The LLC name is there to identify your business v. a or trademark is used to promote your services.
An LLC name must be available in your state so you can check with your state agency for availability prior to the filing.
A trademark is where your name become important and can create value to your business. If branding is going to be important to your business, then you should file for a trademark registration assuming your name is not being used by others in your industry. Check the USPTO website for an initial search.
If your name is (like the marks Apple for computers or Google for a search company), then trademarking the name itself will likely cover the same name with a .com after it. For example, eBay`s trademark is strong enough to cover ebay.com. Anal business owners who are going to rely heavily on their web brand may add .com to their applications.
As far as the services, if there is anything complicated with either requirement, you ideally should get a lawyer. For example, if your LLC will have partners or investors- your LLC structure becomes important. On the trademark side, if there is any issue with someone else already having rights, an application can get complicated and there may be strategies to get it approved.
On the other hand if both matters are straightforward, you can use services such as legalzoom. They do save time and if you find a reputable service provider, you will also get peace of mind that the formation is done properly with a compliance guarantee.
You should also check out www.TheLLCExpert.com
which specializes in the LLC and offers a much faster service. Disclosure- I am a frequent author on that site. So, in fairness to your researching of alternatives, the other major providers in addition to legal zoom are BizFilings.com and corporate.com
Hope this helps