Oh man, this might be a long one...
On top of the formally mentioned projects, the ones that were most inspiring to me over the years are:
UprightsWoody - by Knievel- for his classic design, yet updated slim version. Cleanly built, great for living room friendly placement.
Terminus - by markc74- I really love the shape of this cabinet, and again another Slim. I thought the cab has some really nice lines, and the colour scheme makes for a clean cabinet.
Bella's Arcade - by javeryh- Great construction and wonderful information on painting surfaces. A beautiful theme as well.
The Shmup! Arcade - Ryglore- I really like Ryglore's documentation of this project the most. He really did a great job at putting the process down. Also, he made a fairly unique cabinet shape, and wonderful theme'd artwork. Also, love his joystick mod and custom dust covers.
Aliens Cabinet - Epyx- Awesome theme, great documentation, wonderful outcome. The lighting, to the shape, to the execution, Epyx did an amazing job on this one.
Project Mame - lokesen- All around great cabinet. The artwork and shape stands out the most IMO. But also, it looks completely professionally done! It's clean, well constructed, and overall just looks fricken cool. Though, it's a bit lacking on the documentation.
Bubble Bobble Scratch build - by YoGaBaR- great looking cabinet, featuring Trebeck's wonderful artwork. Though, this cabinet is lacking in details as well, its still nice to look at.
Mission Control v1. - Pixelhugger - Although he's working on v2, I really thought v1 was a great looking cabinet. First, the construction was great, the shape of the cabinet was so unique, and the marquee plexi work was so well done.
BartopsDK, DK Jr., Mario Bros. Bartops - by Jigenjuke- Just outstanding work. One of the first bartop threads I read, and extremely jealous of. Jigenjuke did a brilliant job with this.
Tempest Bartop - by leapinlew- I thought leapinlew did an amazing job with this cabinet. It was simply built, and well documented. The shape of the original tempest cabinet also translated well to a bartop.
UK Dig Dug Bartop - by shrunkenmaster- It's just so cute!
WeeCade - by lokesen- Love the retro look of this little guy. Nice overlay artwork, really well constructed.
POWcade - by endtwist - I thought this was a very classy renovation project. I really liked his use of the side-art as well as the thin-lined chrome/black t-molding.
Galaga Themed Small Bartop - by leapinlew - One of the first bartop threads I read. I really liked the translation of a classic galaga cabinet to bartop. It worked really well.
Metroid Mother Brain Super Console - by SodaPopinksi- Absolutely my favourite project of all bartops!! The theme, the artwork, the details, the MOTHER BRAIN!!!! When I first saw this years ago, it blew my mind.
Atari Xevious Bartop - by retrofuture- I left this one last because retrofuture isn't finished yet! But this bartop will be great once finished, and even in it's current state I found it pretty inspiring.
Cocktail and OtherSega Dreamcast Cocktail table (Michigan theme) - by deadpool18- This cabinet inspired me for my Canucks cabinet. I thought he used the sports theme very smart, not overly done or in your face. Also, a cocktail that runs off a DC is awesome in my books.
Xcelerator - by theCoder- Epic driving cockpit cabinet! Probably the best on the board IMO. The documentation is wonderful, and his attention to details and driving "feel" is commendable.
Woodrail Mini-Pin Cabinet - by froggerman- Classic looking mini-pin. Very well made, well executed...great choices of artwork and colour scheme. Some really good craftsmanship here.
Mini Galaga project - by melon- So awesome. Clever use of the "coin door" access. So tiny, so coooooool!
Vewlix Slim cab - by SpaceHedgehog- I know he's still putting finishing touches on this cabinet, but it's practically done. Great craftsmanship of this replication, and I really love his wiring and mounting of play-components.
Super Mario Bros Wiimote coin block Wiimote tidy - by Franco B- Though not an arcade machine, I give this projects props for the theme and the utility it brings. Definitely inspiring for projects with purpose outside of actual game playing.
I really can go on and on. There are so many great projects here that there are too many to mention...
Great job everyone!