Superior BassWorks (SBW) Deluxe Dirty Gut strings look and feel remarkably like guts... They are a bump set of 6 strings to select from. They are Kevlar core wackers, but they are spiral cut for their whole length, so they move a lot of air and sound very much like gut, or at least like the plain guts that I've played on other people's basses. They have the same thud, but maybe a little more clarity and sustain. Their look and feel is so convincing, I've had a number of experienced double bass people ask me if they are guts.
I started out using a complete set of SBW Deluxe mostly in the medium tension range and stayed with them for quite some time. Their tone is great and they sound wonderful amped, but I finally decided I needed more acoustic volume and clarity with the E and A so I swapped them out for Innovation SilverSlaps E and A (SilverSlaps are the silver colored version of the Golden Slaps mentioned above). The SilverSlaps are clear and loud and they have a remarkable growl. I kept the SBW Deluxe D and G strings; the medium tension gauge and tension match is excellent with the SilverSlaps, the feel is wonderful, and the tone and volume are great. For my playing, I really like these thicker D and G strings.
This SBW Deluxe EA / Innovation SilverSlaps DG mixed-set is what I'm using now, and especially since I've done some sound post work inside my bass, they are providing the volume and clarity that I want for both acoustic and amped playing. They sound great for pizz/slap and arco, although for arco the new SilverSlaps needed 4 to 8 hours of playing, along with a tighter bow, generous rosin and perhaps some technique refinement to work well for arco; in contrast the Deluxe strings are ready for arco right away. When new, the Deluxe strings take a week or two to stabilize, the SilverSlaps only need a few days.
If you're only playing amped or DI'ed, I'd be comfortable recommending the complete SBW Deluxe set, they sound great plugged in. But if you're also playing acoustically, I'd highly recommend the SilverSlaps or Golden Slaps for your E and A strings, or alternatively just trying the complete SBW Deluxe set to see if it's good as is for your bass.
SBW Deluxe string sets are available from Superior Bass Works, or from Amazon, in the very affordable ~$60 range. Innovation SilverSlaps or Golden Slaps sets are available from Innovation or as sets or singles from Gollihur and other double bass specialty outlets. I purchased my SBW Deluxe string set from Amazon and my SilverSlap E and A from Gollihur, both with excellent service. (NFI)