Long tail keyword generator - what do you use?

Hi,
we've built a small SEO tool which combines words to generate long tail keyword terms.
This list can then be copied and send to your favorite keyword research tool for further investigation.

Currently, we have 5 input text boxes for keywords. The tool then combines each line with the other boxes.
(find the current live version for testing in my signature link: then top menu: "TOOLS" > "Long tail keyword generator")


Example:

box 1:
best
cheap
New
Top

box 2:
macbook
tablet

box 3:
reviews
test
Recommendations

You then click a GENERATE button and get this:

best macbook reviews
best macbook test
best macbook Recommendations
best tablet reviews
best tablet test
best tablet Recommendations
cheap macbook reviews
cheap macbook test
cheap macbook Recommendations
cheap tablet reviews
cheap tablet test
cheap tablet Recommendations
New macbook reviews
New macbook test
New macbook Recommendations
New tablet reviews
New tablet test
New tablet Recommendations
Top macbook reviews
Top macbook test
Top macbook Recommendations
Top tablet reviews
Top tablet test
Top tablet Recommendations


That's no big magic, and I was wondering if this can somehow be more improved. I thought about preparing niche related presets, but where do you start or end, and each language has different patterns.
This empty box version gives you endless possibilities, but there is manual work required.

So I'm interested:
How do you build long tail keywords?
Which features would make your day easier to get those phrases?