I've had these Ryka XT Assist shoes for about three months now, and I just love them.  I bought them to do a plyometric workout series (Beachbody's Insanity series) that required a lot of jumping.  My old Rykas weren't cutting it (my arches were in terrible pain during each workout), so I purchased these and have been extremely happy.  They are lightweight and comfortable, and provide really nice arch support.

These provide great arch support for lots of jumping, and also have a nice, wide base that provides good stability for weight-lifting.  I've also been using these for step and kickboxing, and they work wonderfully well for those activities, too.  They are a true cross-trainer!

The base of the shoe also bends nicely, allowing the forefront of your foot to bend easily when doing things like push-ups, where your foot is bent.

As for sizing, I always go a half-size up in my athletic shoes, and did the same in these.  In regular shoes, I wear a 7 1/2, but I always buy an 8 in athletic shoes -- and these in a size 8 were perfect for me.  (With past pairs of Rykas, I've sometimes had to go up a whole size, but these seem to run a half-size smaller than regular sizing.)

I bought these in the gray and red color, and they look really nice, too.

This is the most comfortable workout shoe I've worn in recent years, and I'm definitely going to be buying a back-up pair!

UPDATE ON 3/5/10:  I've been using these shoes since August five or six days a week for all of my workouts, and they are finally starting to give out a bit on the inside.  I usually have to replace my workout shoes every six months or so, so these Rykas have held up really well.  I love these so much that I am buying a new pair of them to replace the ones I bought last year.

UPDATE ON 3/2/11:  Although I still really love these Ryka shoes and went through several pairs of them, I recently "upgraded" to the Asics Gel Intensity , and really like the Asics even more since the cushioning in the Asics is excellent.  That being said, however, the Asics shoes are twice the cost of these Rykas.  If you can afford the difference, though, and want lots of cushioning, I'd recommend trying the Asics.