Again, its not so easy.
Or cheap.

(source)
Disclaimer: I am not am immigration attorney or specialist though we have visited them. This is just our experience with the process so far.
In the US you’ll use an I-129 F form to apply for a K1 visa which gives you the right to marry a US citizen. This way if you intend to switch back and forth between your home countries everything will be much easier (or so we hear). There are ways to get around this route, but we’re playing it safe since we’re not sure which country we’ll be living in yet.
With this form you’ll need a check for $455, a boatload of evidence that you and your intended are actually a couple. We used plane tickets showing trips we’d taken together, credit cards statements showing we spent money in the same place at the same times, emails sent back and forth, the engagement ring receipt, and they allow you 5 pictures. We tried to include pictures of us in different places (AZ, FL, MD) and include photos of us with other people. Mr.D’orsay also created a quick “save the date” to include in the package so they’d know our wedding date and that we’d need the visa before June.
They have a website that will show you the approximate processing times for your center and ours is 6 months. We sent our paperwork to USCIS in October and have received a receipt back, but no further notification. They also have a place online where you can check on your status, but ours really hasn’t been updated (way to keep me stressed US government!). I just checked the site however, and it has changed to say that there is no longer a time frame since they’re exceeding the previous time frame and that they are currently processing applications for the fiance visa from March 2008. Great.
The next step is that Mr.D’orsay will have to go to the US embassy in London for an “interview”. We’ve heard from other couples who’ve done this that the interview is actually like going to the DMV or the bank, its just a window teller that asks you a few questions. Which is a bit unfortunate as we saved wedding contracts etc as addition evidence for this interview. Go figure.
We plan on returning on June 1st which gives us slightly more that 90 days once we enter. This is important because once you enter the country on a K1 visa you’ll have 90 days to get your marriage certificate and get married. Which means come hell or high water we’ll be married before August 29th, otherwise we’ll have to restart the whole process.
In the UK however, I’ve heard it only takes a few months to receive the fiance visa! I have a pretty large family and we can’t really afford to pay for a wedding in pounds, which are a few of the many reasons we decided to get married in the US. Though that “couple of months” waiting period sounds pretty nice!
You can’t work on a fiance visa while you’re in your fiance’s country either. With both the US and UK fiance visas you are not allowed to do paid or unpaid work, which means no internships, volunteer work, etc. Again, on the US fiance visa you have 90 days from point of entry to get married, in the UK they give you 6 months.
That’s our experience in fiance visas, I hope its helped you if you’re on this path and if not I hope you’ve gained some insight.
Have you had any immigrations issues? What advice can you add for other couples in similar situations?