http://msequencer.blogspot.com/
I picked it up yesterday (took the chance and spent the $15) and I already love it. It makes it really easy to sequence multiple apps (and probably hardware, too, but I'm only using it to sequence virtual MIDI apps). Within a few minutes I had a simple tune put together sequencing DrumJam, ThumbJam, SampleTank (2 channels), and Magellan. Magellan didn't play well with SampleTank (I think Magellan is too CPU intensive) so I had to close Magellan.
But what I love about this app is that it makes sequencing super easy (no weird pinching or swiping motions like you need to use in Genome and no bizaree project/pattern hierarchy where you -- or at least I, because I'm slow -- can't figure out what you're editing or saving) but still has enough features in terms of note, pattern, and song editing to be useful. All editing is done through single taps and the interface is super clean and easy to figure out.
It only supports 4/4 time and 16th-note divisions and there's no MIDI file export, but if you can live without those for the time being and if you can't really get into Genome (as powerful as it is) definitely pick this up. It's especially handy paired up with AudioBus synths as it'll drive as many as your device can support. It'll do 90% of what you need a MIDI sequencer for -- and with probably the most robust, cleanest, and easiest implementation of MIDI routing I've seen on iOS -- and the interface is just so clean.